Invisible Spectrum
by lirodendron
Summary: In which Sherlock Holmes wonders what to be if he can't be himself, John Watson has to be someone he wished he didn't, trust is tested on all sides with no margin for error, and complete darkness is just barely held at bay. Part 5 of my Conductivity series (immediately after "On the Polarity of Exotic Stars"). This work contains a sexual scene of dubious consent. Sex and Violence.
1. Chapter 1

Two weeks after their return from Dartmoor everything seems fine. John forgave Sherlock his deeply hurtful comments on the basis that he was drugged and terrified at the time, and when they got home Sherlock made it up to him properly, over a long weekend. Things are going so well, he can almost forget about anything other than their immediate existence together.

 _Almost, but not quite, Mycroft had released Moriarty the same day Franklin had blown himself to bits, things are in motion, it won't be long before something happens, he can't see all ends, but he's been preparing, it's possible he'll be able to contain the damage, that he won't have to scorch the earth, that he and John will be able to remain as they are without interruption, if anyone can manage it he and Mycroft together should be able to, it doesn't bear worrying about at this point..._

It's the middle of the day on a Saturday and they've been following a uniquely nimble cat burglar who, in addition to jewelry and cash also takes old family photographs, even staying an unwise amount of time in the houses after he's found the valuables in order to locate them. Unfortunately, the man seems to have just gotten wind of them and is now running for it.

Sherlock breaks into a sprint and hears John do likewise. He can easily outpace John when walking, but at a dead run John is ultimately faster. He's not surprised, then, when John flies past him in only a few moments. They skid around a corner after the suspect, ending up in a wide alley. He's fast but Sherlock suspects he's lacking in stamina. They shouldn't have much trouble catching up.

John is indeed gaining on the man, with Sherlock just keeping up when everything goes dark. Completely dark, like a light switch being flipped in a windowless room. Before Sherlock can even fully register what's happened, he stumbles and slams into the pavement.

"Damn it, he went up!" He hears John curse from somewhere up ahead. "We'll never be a match for him on the roofs. Bloody acrobat."

 _Sherlock barely notices the words, dark, why is it dark, there is nothing, nothing at all, he blinks but it's all the same, he can't even see John, though he can still feel him at the back of his mind, blind, blind, how can he be blind with no warning, it's preposterous, and yet no matter how hard he looks he can't see anything, what if he never sees anything again..._

He feels himself starting to spiral and grounds himself quickly. Pavement beneath his hands. The moist, acrid scent of London air after a first good spring rain. The sound of John's feet trotting towards him with urgency.

"Sherlock, what happened? You all right?"

He's stayed down just long enough to trigger John's concern. That won't do. He shifts just slightly so John can't see his face, and pretends to be inspecting his foot. "Yes, of course," he says calmly. "Uneven paving stone."

 _John mustn't know, not yet, not until Sherlock's thought it through, not until he understands what's happening to him, he has to think and he won't be able to with John worrying at him..._

"Help me up, please. I believe I've injured my ankle."

John hauls him up and as he does so, Sherlock rolls his ankle, hard. John will insist upon examining it and there will have to be some swelling.

"The mighty Sherlock Holmes, taken out by a lowly paving stone...Can you put weight on it?" John asks.

Sherlock makes a show of trying and lets out a little grunt, calculated to convince John that it's giving him a great deal of pain but that he's trying be stoic.

"Christ, that's not good. Here, lean on me and we'll try and get a taxi home." John slings Sherlock's arm across his shoulder and helps him hobble towards the nearest main road.

 _Perfect, the less John sees of his eyes the better, now John's got a focus, he won't be looking for anything else, it gives Sherlock time..._

In the taxi, Sherlock turns his head to the window and scans his eyes back and forth, unseeing. John assumes he is thinking of how now to trap their aerially gifted larcenist and lets him be. When they arrive home, John helps him up the stairs and to his chair. He examines Sherlock and pronounces it just a mild sprain, based mostly on Sherlock's faked reactions to his manipulations. He wraps it efficiently and orders him to keep it up with an ice pack on it for the rest of the day.

Sherlock is more than happy to comply. That will avoid him having to navigate the flat too much. He's memorized it well enough, but things do get moved and he wouldn't want to trip and give himself away.

He thanks John, with just enough of an edge of sarcasm to keep him from getting suspicious, and tilts his head all the way back, closing his eyes.

 _Now he can panic, John won't question him in this posture, as long as he doesn't move he can let it overwhelm him as it will eventually no matter what, let it cycle through as many times as it needs to until it subsides, like being stuck in a washing machine of fear, he hates the dark, so boring, so empty of data, he should focus on his other senses but the darkness keeps drawing his attention back, the void, the physical manifestation of something that has stalked him since he was a child, and he thought once he had John it meant he'd escaped it, it was unable to withstand John's brightness, but now here it is again and not even John has light to drive it off, he'd left it and it's come to claim him now, blindness is just not being able to see, he knows, but that's not what this feels like, it feels like being dragged back down to what he'd thought he was free of, he has no anchor when he's like this, why can't he see John at least, that part was always technically just in his mind, not through his eyes, it should still work even if his eyes don't, does this mean his brain is malfunctioning, what else might be wrong, what else might he lose, his reason, his intellect, would he even know it if they left him..._

It goes on like that for hours, Sherlock trying to think his way out of the hysteria and almost making it. But the darkness is still there, no longer a thing that lurks in the back of his psyche, tightly under guard, but now literally surrounding him, fully manifested in a way he can't flee, ignore, or fight. What he wouldn't give for any kind of opiate right now, anything to slow him down. If there were some in the flat, he'd probably succumb, calling it medical necessity, but he can hardly ask John. Saying it was for the pain in his ankle would never work. John knows a junkie's gambit when he hears it.

Just when his brain seems about to literally tear itself apart, the thrall breaks. Not entirely. Just enough for him to get a foothold, to begin to force it back in the locked basement rooms where it belongs. It must take hours for him to get it under control, if not completely silent, because by the time he's back to himself properly, he can no longer feel the afternoon sun on him. Sometime after 6pm, then, although he can't be any surer than that. He loses time so easily.

John is in the room, typing on his laptop, and is probably distracted enough that Sherlock can risk moving. He gets up slowly and, being careful to limp a little, makes his way through what he hopes is the obstacle-free path to the bathroom. He reaches it without incident and splashes some cold water on his face. Now he has a dilemma.

Sherlock can feel the stubble growing in on his cheeks. It's like microscopic spiders crawling over his face. He shaves twice a day just to avoid the sensation, unless he's out on a case or undercover. Such activities make him forget about physical unpleasantnesses like facial hair, body odours, dirt, grime, and rough clothing against the skin, at least until they are over and his attention is no longer taken up entirely with the work.

 _He's always been like this when not high or working hard, sensory issues, some people call it, the seam of a shirt rubbing against him, dirt under his nails, grease in his hair, being touched with more than a handshake by most people, they all set up an unpleasant tingle in his brain, make his skin crawl until he wants to tear it off of himself, sometimes it's even physically painful, he's learned to cope with it through fastidiousness, keeping strong personal boundaries, avoiding certain textures and fabrics, it mostly works, and now he has John who never sets those sirens off, knows how to silence them for him, at least temporarily, but right now he has no way to distract himself from the itching and burning, he can't shave blind and he can't bear not to, he's only just gotten a grip again..._

He'll have to tell John, he realises. He would have had to at some point anyway, and he'll need John to help figure out what's happened and why, and hopefully reverse it. It might as well be now and reduce the risk of his own nervous system pushing him over the brink as well. He's far too near it as things stands.

"John!" he calls calmly. "Will you come in here, please? I need your help."

He hears John get up and pad towards the bathroom, probably assuming Sherlock needs a hand climbing into the shower or something similar. Sherlock faces the mirror, eyes closed and hands on the vanity supporting his weight.

"Okay..." John says slowly, after assessing his posture. "What's wrong?"

"John, I am going to tell you something and then I am going to ask you to do something for me." He keeps his tone even. "It's very important for me that you not react immediately to what I'm going to say, however much you might want to, and just do as I wish without asking me any questions right away. I cannot process an emotional outpouring or speak at length right now. Can you do that?"

John instantly puts a hand on Sherlock's back. "Of course," he says, but in the voice he uses to keep others from noticing that he's afraid.

"John, I cannot see. Not you, not your light, not at all. My vision is completely gone."

John's breath catches in a combination of relief and shock. He swallows and Sherlock can hear him open his mouth with what are surely a dozen questions and exclamations, but he bites his tongue.

"It happened very suddenly in the alley. That's why I tripped." That's really the only information he can give John at the moment.

John takes a deep breath, like he's trying to hold everything in. "What do you need me to do?" he asks, his voice hardly wavering at all.

 _John, so reliable, so disciplined, his doctor self, his lover self must be screaming at him to fix it, to find an answer, to diagnose and to fuss over Sherlock but he stops himself, because Sherlock has asked him not to, he's making himself be the soldier for Sherlock because that's what Sherlock needs..._

"Shave me."

"What?"

"John, I need you to give me a shave. I can't use a straight razor blind and your electric one doesn't cut close enough."

John knows why Sherlock needs this, but is still hesitant. "Sherlock, I've never used a straight razor before, much less on someone else. I might hurt you."

"Oh please, you're a surgeon. You have steady hands and you can handle a blade. Just do... the opposite of what you do when you operate on someone."

"Sure, simple," John mutters under his breath. "All right, well, sit down..."

John knows the ritual, even he doesn't partake himself, he's seen Sherlock do it hundreds of times, understands how important it is for Sherlock's state of mind. Especially right now.

Sherlock sits and waits patiently. John fumblingly whisks up the lather in Sherlock's shaving bowl, but applies it correctly in smooth, circular strokes and doesn't get any up Sherlock's nose. He wraps Sherlock's face in a hot towel and the scent of eucalyptus, combined with the sandalwood from the soap, is instantly calming. When it's time to remove the towel, John wipes the dirty lather off his face with it tenderly, and the touch of his fingers is instantly calming as well.

 _It's amazing how the right touch from John can dispel a thousand other busy thoughts, like how a stone dropped into a pond erases the reflections in it, all the voices and images flying about his brain stop and are replaced with a single word, a single thought, John.._.

John lathers him again and Sherlock can feel the tension in John's body against him as he approaches with the blade. Still, his hands are rock solid and confident when he starts at Sherlock's left ear and works down, shaving with the grain of the hair. He's working very slowly, but making no mistakes. He does across Sherlock's face and under his nose, then tilts Sherlock's head back and, with a deep breath, starts on his neck and throat.

Sherlock's been shaved by barbers and servants many times before, though most often these days he prefers to do it himself. Some might be surprised at that, he supposes, given his dislike of physical contact with all but his closest associates, surprised that he's comfortable letting a stranger hold a blade to his throat. But the distant professionalism of the situation reduces his agitation, rather than increasing it. And, Sweeney Todd always excepted, most barbers are motivated not to cut up their clients. This, though, is different.

 _So different, it's his friend with the blade to his throat, the trust required to allow someone you know to do this is far deeper than needed for a trained coiffeur somehow, and he trusts John completely, his hand sure and his touch tender, his breath sweet on Sherlock's neck, his thighs pressing against Sherlock's as he straddles him to get the right angle, no other shave has ever been like it, Sherlock keeps his eyes tightly shut so he can forget the reasons that John has to do this at all and focus on him, on the familiar yet unfamiliar rhythm..._

John is meticulous, make sure he's not missed a spot before stopping, replacing the towel, then repeating the whole process, going against the grain this time. Then a final hot towel and the sting of aftershave. Sherlock hisses sharply, but is glad for the bracing shock to bring him out of his trance. Finally there is the soothing feeling of John's palms massaging Sherlock's musky-junipery lotion into his skin.

Sherlock reaches up and runs a finger across his cheek. It's as smooth as anyone's ever got it before. And not a nick on him.

"Thank you," he says, trying to convey his sincerity in his voice. "It's... very good."

"You're welcome," John says, but then tension comes back into his tone. "Now, Sherlock, please, I need to know-"

Sherlock holds up a hand. He can't think about it again right now. His mind needs a break. "Not yet," he tells John testily. Then he softens his pitch and speaks quietly. "Please, John, I know we have to but not yet. I need to rest. This...hasn't been easy. Tomorrow, I will make myself fully available for your inquiries and examination and anything else you deem necessary. Just let me rest for tonight."

John agrees, although Sherlock can tell that it costs him. He doesn't attempt to help guide Sherlock into the bedroom, although Sherlock can feel John hovering in case he should be in danger of running into something. Sherlock refuses to put his hands out and feel his way. He undresses, and then stands in the doorway facing where John should be. "Sleep with me," he says.

John's voice comes from the other side of the kitchen than where he'd calculated, and he feels a flash of frustration at his mistake. "Yeah. Yeah, of course. But in the morning, we really have to deal with-"

Sherlock turns away and climbs into bed before John can finish that sentence. John joins him in a moment, and it is reassuring. He expects sleep to be a challenge, but his mind and body are so worn out from the day that it takes him before he even has a chance to notice he is fading.


	2. Chapter 2

Sherlock wakes suddenly and tries to open his eyes. It takes him a moment to understand why he can't seem to manage it, and isn't quite able to suppress the sharp intake of breath the momentary panic causes.

John is with him, instantly, hand on his arm. "It's okay. I'm right here."

 _John, it's so unnatural to have him near, to think of him, without the accompanying glow, the aura that assures him everything is all right, even when John's gone it's still in his mind, but now there's just nothingness..._

Sherlock sits up, slowly swiveling his legs over the side of the bed, acclimating himself to the darkness once more. He feels John get out of bed too and hears him rummage through his wardrobe.

"I'm going to examine you," John's voice says firmly, from immediately in front of him.

He is not asking for permission but Sherlock nods anyways, and submits coolly to the standard poking and prodding, the cold stethoscope, the thermometer in his mouth.

"Well?" he demands impatiently when John is done.

"Well, you didn't have a stroke..."

"If you thought I had we'd have been in the hospital yesterday."

John sighs. "There's nothing wrong with you."

 _Everything's wrong, doesn't John realise that, he can't have found nothing, this doesn't just happen..._

"Of course there's something wrong me, I can't see!" Sherlock shouts, agitated.

He feels John's hands on his thighs. John is kneeling before him. "I know, I know. Just... you're in perfect health. Your vitals, your reflexes, all as they should be. Your eyes look completely fine, they're responding to light stimulus normally."

"What does that mean?"

"It means we're going to have to get a look at your brain. I'm afraid it has to be something effecting the visual cortex. You need an fMRI so we can see what going on up there."

Sherlock had suspected as much, at least that some kind of scan would have to happen. He didn't know of any diseases of the eye that would cause instant blindness like that, although he'd rather been hoping John did. "You do it."

"Me?" John gives a nervous laugh. "I'm not a brain specialist and I certainly don't know how to run an fMRI machine! Of course I'll go with you, and I know just the doctor you need see, she's completely brilliant, you can trust her-"

"No. I don't want anyone else knowing," Sherlock says urgently. "You know what enemies I have, John. It will have to be you."

 _If Moriarty were to find out about this, how helpless and vulnerable he is, how long would they last, what if he took John again, Sherlock couldn't get him back, Moriarty could kill Sherlock easily like this but what's worse he could torment him, reducing him to begging, tricking him into hurting someone, many people would love to take advantage of his situation now, but Moriarty is the only one he fears..._

John takes his hands. "I understand, okay? I do. And I'm flattered that you think so much of me, but I can't do everything. It's impossible. And if you want your sight back, you need to be seen by people who know what they are doing."

"Unacceptable," Sherlock snaps. "I'll be a target, instantly. I already am."

John jumps to his feet in frustration and Sherlock can picture him clenching his fists at his sides so as to not say something he'll regret. "How about Molly?" he asks after a few seconds. "Can Molly know?"

 _She'll probably be unbearable, fussing over him, being upset, emotional, far worse than John, at least John knows how much it bothers him, shows restraint, and even when he doesn't he's not as bad as her, but she's trustworthy and loyal and that's the important thing..._

"Does she know how to run the scanner?"

"I doubt it, not very much cause to look at brain activity in dead people. But she can probably find a technician who has no idea who you are and schedule it at time when no one will be around. I won't put your name on anything. Molly can run the blood tests through the lab anonymously and I'll show Caroline the scans after you've gone. You'll be my Patient 1, that's it. And no one who knows you will think anything of you being at Bart's at odd hours. Good enough?"

Sherlock consents, reluctantly.

"Good. Okay. I'll make some calls. Do you... need help with anything?" John asks delicately.

"You won't have to bathe or dress me, if that's what you're asking."

"Hey! Don't start that," John barks. "This is. Not. My. Fault. If you can't accept help, this will not work. Got it?"

Sherlock sniffs, but murmurs his acquiescence. It takes him longer than usual to navigate his ablutions, but it's doable. He tries to seem more grateful when John helps him with shaving again, without being asked. John doesn't say anything either, but ruffles his hair affectionately when he's done. Sherlock does feel a bit of satisfaction when he goes to dress, that the sock index and alphabetized wardrobe are useful for more than just taming his compulsive side.

 _White shirt, third from left, second best trousers, lower bar, centre, charcoal jacket, top bar right, matching socks, second row back, fifth from the left, shoes, matte black leather, wardrobe floor..._

Just trying to do simple tasks without fumbling about suddenly takes up so much of his concentration that when he's done he's shocked to realise he hadn't thought of anything beyond what he was actually doing. It's disconcerting, but before he has time to worry about it, he find he's got the opposite problem. He can't think of anything to _do_ but think.

 _Can't read, can't work on his website, can't take cases - even if he could do casework like this his condition would get out - can't watch telly properly, can't run his experiments, can't research, can't defend himself, can't protect John..._

John interrupts this depressing string of can'ts. "We'll go in tonight, at 11 pm. Molly knows a guy and the place will be all but deserted."

"What I am supposed to do till then?"

"Oh, you're welcome," John says irritably. "I don't know, Sherlock. Organise your mind palace? Listen to the news? Play your violin."

"I can't read the sheet music."

"Yes, and you've memorised nothing and never compose!" John shouts, then falls quiet. After long moments of silence he comes over and puts his hands on Sherlock's hips, sighing deeply. "I'm sorry. I know this is devastating for you. The truth is, I'm afraid too. But we will figure this out. Until then, how about I try not to take it out on you if you try not to take it out on me?"

"I...suppose..." Sherlock agrees. He finally works up the courage to ask what's been eating at him since yesterday. "John... could this be... something worse?"

 _Is he dying..._

"Sherlock, we can't know–"

"Don't lie. Tell me."

He can feel John fidget uncomfortably. "Yes. There are a few things it could be that are serious. I mean, more serious than losing your vision permanently."

"What are they?"

"It could be a tumour. I'm sure you've thought of that. It could also be an aneurysm or a blood clot. You travel. It could be a parasite or virus causing encephalitis." John adds quickly, "But you haven't had any other symptoms so I really don't think–"

"I see. Thank you for telling me. Will you please hand me my violin?"

John does as he asks. "If you like, I can read to you later."

Sherlock nods in acknowledgement, closes his unseeing eyes, and tries to lose himself in the music.

At the hospital John takes him to a private room and orders him to change.

"I am not wearing a hospital smock," Sherlock declares. "They only need to look at my head, anyway."

"And if I could cut it off and stick it in the machine, we'd be in business. It's a giant magnet, Sherlock. And your shirt has metal buttons. Not to mention your trousers. As entertaining as that would be, I feel the hospital smock is probably the path of least embarrassment. Change, I need to go talk to Molly."

Sherlock does, with bad grace. He's freezing and the smock was clearly not designed for a man of his height.

 _Alone, in a strange room, no context, just draughts of recycled air and the smell of antiseptic, it's silent and still and artificial, it throws off his whole sense of his surroundings, things are okay in his flat, and okay when John is there but now he's just untethered, at the mercy of his environment…_

He's ashamed of how relieved he is when John returns.

"All right, they're ready. Don't say anything, she's told the tech you're some kind of American bigwig, and that's why you don't want anyone to know about this. Also, be nice to her – I think she's taking one for the team."

"What?" asks Sherlock, confused.

"She agreed to go out with him."

" _That's_ enough inducement for him?"

"One: Don't be an arse. Two: If you could see him, you'd understand."

That sobers Sherlock quickly and John takes him into the fMRI room. Sherlock keeps pace with him, letting John's shoulder touch his arm just enough that he can follow John's movements without the humiliation of public guidance. The room feels big and empty, with a loud, low electronic hum pervading it. John shows him to the table and has him lie down, face up.

 _Vulnerable, cold, like a corpse on a slab in the morgue…_

"Now, you have to stay completely still. No talking, no moving. I'm not supposed to stay in here, but if you want…"

Sherlock shakes his head, even though for once he'd really prefer John stay.

"Okay, well I'll be in the booth then. I'll be able to hear you if you need me." He hears John walk out of the room and the door close. It's even more discombobulating to be lying mostly naked in the centre of an empty space like this, not allowed to move around, to speak, and he tries to focus on something else.

Presently, the machine starts, a deafening but smooth whir, so deep that it feels like it's vibrating inside of his bones and teeth. John's voice comes over the intercom, audible but muffled by the noise of the scanner. He's telling Sherlock exactly what's happening. It's reassuring to have his voice, but too much work to pay attention to. Trusting that John is watching out, he turns inward, returning to the case of the cat burglar.

 _The problem was predicting when he'd strike, they'd tried tempting him with high profile jewellery purchases, profiles of homes full of antiques, but he never took the bait, no, too smart for that, they'd wasted nights lying in wait for him, it had to have something to do with the pictures, but what, and how to turn it against him…_

He manages to successfully block out the noise of the spinning magnet, the emptiness of the room, and finds himself startled when a cool hand touches him on the arm.

"Sorry, my fingers are always freezing," Molly says, her voice oozing pity. "John's making copies of the scan and then is going to consult with his doctor friend. Can't imagine she's thrilled at being dragged down here this time of night. Anyway, do you want to wait in the lab… or I can take you home, if you like?"

 _He seethes at the necessity for this, the total dependence on others, being shuffled around like an extra piece of furniture…_

"Clothes," he says curtly. "Then lab."

He gets to his feet, hoping the hospital smock hasn't revealed too much in the process. He's casual about nudity in general, but here he already feels too exposed, and he tends to modesty in front of Molly, if only for her own sake.

"Uh…right…" Molly stammers and grabs his hand. "Um. Are you… are you okay? Because if you want to… talk about… I mean, I just know it can be quite… um…"

Sherlock shakes her off. "Perfectly fine. And I don't need to be led around like a feebleminded child. I remember the way, and even if I didn't I could easily follow the sound of those ridiculously painful shoes you're wearing because you think they make your rather flat bottom more attractive and the smell of your over-applied chemist shop perfume."

"Right. Right. Of course. I… um… came from a date. Not the technician. A nice guy…"

"Clothes!"

She scurries and he follows as sedately as he can manage.

 _He does remember the way, at least back to the first room, from there he could probably get himself to the lab, he's walked these halls enough, but he couldn't do it without fumbling for a door handle or the curve of a wall at some point, if he made a wrong turn he'd be done for, unmased, but he doesn't want to be seen to be led either, even if he hates it having Molly as a beacon, showing the way, opening doors, is probably the least invasive form of assistance he's likely to get…_

At last he is back in the lab, which provides a modicum of familiarity even if the equipment in it is largely useless to him. He waits, silent and straight-backed, for John to return. After a few attempts Molly eventually gives up on conversation and goes quiet to wait with him. He finds himself unexpectedly relieved she doesn't leave, wanting privacy but still averse to being left alone. As thanks he refrains from shouting at her for the irregular finger tapping she's unconsciously engaging in.

It must be more than an hour before John finally arrives, his restrained, almost stiff-gaited footsteps a welcome sound and his voice even more so.

 _He sounds tired, and like he wants to rush over and take Sherlock in his arms, but he won't do that here, probably wouldn't even at home because he knows Sherlock might not be in a place to accept that right now, and it's true, but the thought that John wants to do helps, even though he knows before his friend says a word about it that it's not good news…_

Sherlock waits for John to speak. He does not say any of the things Sherlock expects.

"Your brain is fine," he tells Sherlock, standing close enough the Sherlock can just detect the warmth of his body. "No damage, no tumours, no swelling. You're not… well, nothing obviously structural seems to be amiss."

 _John's relieved, he'd thought Sherlock might be dying too, he'd thought they might find out the worst, but he'd hid it cleverly, only been able to because Sherlock wasn't able to detect the glitches in John's glow that would have alerted him, now that there is no glow, but John can't hide it any more, doesn't need to, still he's not happy, he's frustrated, reluctant to say more…_

John pauses too long. "In fact… your visual cortex is responding normally."

"I don't understand," Sherlock says flatly.

"In the scan… it was lighting up just like it would if you were receiving visual input. Caroline said—"

"Oh, Caroline your ex?" Sherlock asks nastily.

"Sherlock…"

"No, really, if it weren't obvious enough from the fact that she was willing to run down to the hospital after midnight just to do a favour for you, I know what you smell like when you've been around a woman you've shagged."

 _He's being unnecessarily cruel to John, he knows it, but he doesn't know what else to do when everything is so completely out of his control, upside down, incomprehensible…_

"It was medical school. She's married. And she's the top rated neurosurgeon in London," John says coolly. "Caroline says your brain scan is indistinguishable from that of a normally seeing person. There's absolutely no detectable reason you should be blind right now."

Sherlock leaps up and steps back from John until his back hits the bench behind him. "You think it's psychosomatic, don't you? Like your sham limp. You think I'm… what? Losing it, finally! Psychologically crippled. Damaged. Hysterical blindness, isn't that what they call it? I'm just hysterical!"

He's breathing hard and his voice does have a hysterical edge to it. He knows he should calm down, but to not be believed like this, it makes him feel trapped, helpless, more so than just not being able to see.

"No." John steps aggressively toward him. "No, Sherlock, I do _not_ think that. There was a reason I had that limp, you know what it was, and I _was_ damaged, crippled. Unless there are things relating to this you haven't told me, I can't see why this would be psychosomatic. Are there things?"

"No…" says Sherlock slowly.

 _There are things he's not told John, probably too many, things that worry him, things that he fears, things that might happen that he's not sure he can prevent, dark things from his past, but none of them seem to have any connection to the loss of sight…_

"Good," says John. "Then we're going to continue on the assumption that this is a medical condition. Not everything shows up on a scan. Blood tests will tell us more. Now, let's go home."

Sherlock nods, slowly returning to a state of equilibrium. He hears Molly stir, and wishes she hadn't seen that. She's got his coat and helps him into it. He cringes when she opens her mouth to speak, but instead of sympathy she just says very quietly, low enough that John can't hear, "You're still yourself, you know. This doesn't change that."

"What?" His head snaps sharply in her direction by reflex, but she doesn't say another word and slips quietly out of the room.

It's two in the morning by the time they get back to Baker Street and neither of them are in the mood for sleep. John insists on picking up some takeout. "I'm not letting your starve yourself until we figure it out. If you have some kind of disease, not eating will only make it worse."

Still, neither manages to do much more than pick at the food. They sit in silence, lost in their thoughts until finally John slams his hand down on the table. "Enough of this."

Sherlock runs his hands through his hair, tugging on it, and tries to give John his attention. "Enough of what?"

"This. What to do we do? We solve mysteries. This is just a medical mystery. You're a detective, I'm a doctor. Who better to solve this one? Let's get to work."

"I'm really not in the mood—"

"In the mood to what? Get your sight back? Now, work you stubborn arse."

 _John's right, he's not been thinking about it at all, he's been avoiding thinking about it, allowing other people to do it for him, hoping for a quick fix or at least a diagnosis, letting himself be made irrelevant to his own problem, but now it's clear it's not going to be simple, not going to just go away, he can't leave it in the hands of others…_

John gets up from the table and Sherlock hears his chair creaks as he settles in it. Sherlock follows suit. The ritual helps.

"First thing," says John. "Have you ever had any problem with your sight before?"

"No."

"Did you have any symptoms or feel unusual leading up to this?"

"I told you I didn't."

"So what do you we need to look for?"

 _John treating him like he's never deduced a thing before, but he can't quite resent it, his brain is shying away from this, away from what it all might mean, he needs to be forced to do it, to solve it, because maybe no one else can…_

"New factors."

"Okay. Let's start with the past few weeks. What's new? Everything. List it."

"I changed tailors, Mrs. Hudson got a new cleaner for the floors, we ate at that Irish pub with the filthy toilets, you went to Paris to visit your old professor and came back with that knock-off watch and Italian leather shoes, nice choice by the way, perhaps some sense of style is finally rubbing off on you, that miserable potted fern finally expired, I had two cigarettes while you were gone and they weren't my usual brand, we met three new clients, we staked out two mansions unsuccessfully, one of which was unusually musty, you switched the brand of coffee you buy us, which you should definitely switch back immediately, I was sneezed on by a music student on the tube, I changed my violin strings, the firewood Mrs. Hudson bought was fruitwood instead of walnut, one of the corpses at the morgue I was experimenting on had died of unknown causes, and Lestrade forced an unknown brand of whiskey on me after I solved that brank fraud case from Chessington."

Sherlock says of this very quickly in a single breath, before he's even consciously put it together in his mind. He takes a large gulp of air and allows himself a moment of happiness that his brain still appears to be in working order as far as memory goes.

"Right…" says John slowly, taken aback. "Well, some of those could be worth looking into…The violin strings are probably fine, but maybe the dodgy food or an allergic reaction to the cleaner? Mould in that house?"

John's reaching, but they don't have much in the way of leads. Sherlock nods in what he hopes is an encouraging manner.

"What about…substances?" The slight hesitation makes it clear to what John is referring.

"I told you that was done."

"I know… Just… people have relapses. I won't be angry, but you have to be honest with me. You've scrambled your neurons enough, who knows what a bad batch of something could do?"

"It's. Done."

 _And it is, although so many times it's nearly not been, he's ashamed to admit he was thinking of it as recently as yesterday, still he hasn't succumbed so it doesn't count, and something he almost but didn't take isn't relevant to the investigation…_

John appears to accept that. "Anything else? Anything biological or chemical either of us has been exposed to? I mean, you did point out you have enemies… could this be intentional…?"

 _Intentional, maybe, it wouldn't be that hard to poison Sherlock, it's not like he has his food tasted, but he'd like to think he'd notice something was off, biological, London's an international city and he's out in it, in its guts, who knew what was floating around there, exotic diseases, recombinant viruses, impossible to track them all down, but he didn't feel sick otherwise, unlikely, as for chemical…_

"John!" he practically shouts, getting out of his chair and in one smooth move jumping on to the seat. "Chemical!"

"Chemical…" repeats John pondering. Then Sherlock hears his breath catch and they say it at almost the same time.

"Baskerville!"

"Obvious!" Sherlock curses.

"Wait, is that possible?" John asks. "I thought it didn't stay in the bloodstream long at all. Plus, I'm fine."

"You tell me," Sherlock says. "You're the doctor."

"You're the chemist," John mutters. "Well… everything has a half-life, so depending on what it was, small amounts could still be in your system. They could have been lying about how long it persists so we would leave and forget about it."

"Likely," Sherlock agrees. "However, as you pointed you're fine and I'm not hallucinating, fearful, or aggressive."

"Well… perhaps it's having a sort of aftereffect on you. Your brain is… different."

"Drug addled?" Sherlock snaps.

"Occasionally," John replies calmly. "The drugs could have done some reorganising up there. But I was actually referring to your extreme intelligence, powers of memory and observation, your synaesthesia, and all the other things that make your mind unique. Sherlock, your brain isn't like anyone else's in the world. There's no reason to think it would react like it. The Baskerville drug… it's a possibility."

 _John's made him do it, helped him work as he always does, they've found a lead, he's so grateful, he doesn't even mind John harping on the drugs or hinting at his supposed mild autism, he wishes so badly he could see John now, see his kind face, see what colour he is, how bright, how strong, but even the lack of all that can't dim the warmth he feels right now…_

"So, now what?" John asks, shaking him from his reverie.

"We'll need a sample."

"How are we supposed to… Oh. Mycroft."

"Mycroft," Sherlock confirms grimly. "He's going to want to know why."

"Hmmm," John considers. "Do you want him to know?"

"I really don't. He'll only meddle."

"Well, if you like I can try asking him?"

"You?" asks Sherlock incredulously.

John shrugs. "It won't be coming from you that way. I think I have some ideas on how to talk to him…"


	3. Chapter 3

"Mycroft, it's John Watson. Yes, of course you knew that, how ridiculous of me to even bother with basic manners. As a matter of fact I do want something. It's a bit of a massive favour. Well, by my calculations you owe me a bit of a massive favour. Or three. Oh really? Would like me to list the ways I've kept your brother alive, clean, and out of jail over the past two years? All right, _mostly_ out of jail, I'm not a superhero. A sample of the drug from Baskerville. You _know_ which drug. And its molecular formula. Professional curiosity. Christ, Mycroft, you think I'm planning on fashioning a hallucinogenic bomb and making all of London go mad? I'm asking for an ounce or two. See, I think you _can_ , whether or not I give you a better reason. No, Sherlock didn't put me up to this. I have concerns as a doctor to the long term effects on myself and anyone else who's been exposed. Well, you'll excuse me if I don't entirely trust the word of the chaps at Mad Scientist, Inc. Like hell it has. Goddammit, Mycroft, I have never asked you for a single fucking thing, so just get me the bloody drug, shut up, and trust me! Fine. Fine. Fine! I'll sign whatever you like. No, today. It's Dartmoor, not the moon. Fine. Pleasure. Bye."

 _Listening to John shout at his brother over the phone is highly entertaining, few people other than him ever stood up to Mycroft like that, and in some ways John was better at it than Sherlock, there was no family baggage, no younger sibling dynamic that nearly always made Sherlock seems just the smallest bit petulant no matter how hard he tried, John just took Sherlock's part automatically, thoughtlessly, had done even before he'd really known him…_

John slams his mobile down on the table harder than is wise. "Okay," he says, still breathing loudly through his nose in annoyance. "He's doing it. It'll be at be at Bart's by the end of today. Do you think he bought my reasons?"

Sherlock snorts. "Of course not. He knows something is going on, but he's choosing to let you handle it for the time being. You will be watched, though."

"What else is new?" John grumbles. "Might as well have let you talk to him."

"If he'd have talked to me he would have deduced what was wrong precisely within thirty seconds, and in that case I doubt he'd be content with a laissez-faire policy."

The awkwardness of John's pause is practically audible. "You know, I don't trust Mycroft either… but he loves you and he has resources I can hardly imagine. I know you hate admitting weakness to him but it might not be a… terrible... idea to let him in on this."

Sherlock shakes his head vigorously.

 _He's already counting on Mycroft for too much, he trusts his brother with his life, but that only means he'll do anything to keep Sherlock alive, up to and including destroying everything else Sherlock wants or plans, if given an inch he swoops in and takes control and fixes things in a way that's not always how they should be fixed, and he's far too proud of the army at his disposal, his pride blinds him…_

"My brother himself is bad enough, even if he's genuinely concerned with my health. But I don't trust his resources, and I don't trust him to be able to resist using them. And that could be disastrous."

"All right. You know best." The silent "for now" of John's reluctant acceptance is painfully obvious, but Sherlock lets it go.

He fidgets impatiently in his chair. The end of the day seems like years away. The boredom is starting to creep in on him again, and with it the tendrils of fear of the darkness. Sherlock could work on the cat burglar case some more, but without the ability to go after him, what would be the point?

John senses his mounting anxiety and comes over, sitting down in his own chair and moving Sherlock's feet from the cushion his lap. "What are you going to do until we have the drug to work with?" John asks, rubbing them in a calming fashion.

Sherlock doesn't answer, knowing anything he says would make his distress more obvious.

"I was thinking," John says, running his hand from Sherlock's stockinged foot to up along his calf. "That as once we have the drug a cure likely won't be long off, perhaps we ought to take advantage of your lack of sight for the moment."

"Advantage?" Sherlock snaps, offended.

"Yes," John answers placidly. "You know, the heightening of other senses. If you'll recall you tried that once with me…"

Sherlock finally catches his drift.

 _After a deposition, John had been wearing the least attractive shirt and tie combination Sherlock could conceive of outside of the circus, it had offended his sensibility so greatly that as soon as they'd got home he'd ripped the shirt off John and handcuffed him to the bed, using the offending tie to blindfold him on the basis that he clearly wasn't using his vision anyway, keeping him naked and spread eagle while Sherlock teased every nerve John had until John had begged Sherlock to finish him…_

Sherlock hesitates. Even the ghost of the memory is enough to turn him on, but it feels his current predicament is too serious for that sort of activity at the moment. There's too much to worry about, too much that could end badly if the Baskerville drug isn't the answer.

"Come on," coaxes John, still caressing his leg. "Sulking all day is only going to make you edgier, and neither of us has anything better to do but wait and get more and more wound up. Why not release a little tension instead? I'll make it worth your time…"

Sherlock becomes aware that even if his mind is far too wound up and cluttered to contemplate John's proposition, his body is most certainly listening and is enthusiastically in favour of the idea. Sometimes, it is best to listen to one's urges.

Sherlock makes a very low sound of assent, and John pulls him to his feet with an arm around his waist. "Get undressed. Get in bed."

 _It's always lovely when John has a plan, even now when Sherlock is far from in the mood to play, he decides to let John do whatever he wants, perhaps he'll get drawn in, perhaps it will distract, as least for a minute or two…_

He does as he's told and John joins Sherlock on the bed presently. "Smell," he says, holding a finger under Sherlock's nose.

"Coconut oil," Sherlock answers promptly. "Pleasant."

"Good. Now roll over."

Sherlock turns onto his stomach. John promptly straddles his waist and Sherlock is made vividly aware that John is also completely naked.

John dribbles some of the warmed oil between Sherlock's shoulder blades. He leans down and whispers in Sherlock's ear. "We're going to test your senses. You have to tell me exactly what I'm doing as I do it."

 _Oh, a game, he loves games, particularly these kinds of games, how clever of John to think of something to take his mind off his impairment, he'll happily play along for as long as John likes, or as long as he can stand, whichever comes first..._

It's unfamiliar, verbalising like this, but Sherlock does his best. "You're spreading coconut oil over my upper back and shoulders with your hands. Now you're rubbing my neck, working your fingers up into my hair and running them down into my shoulders, pressing into the muscle as you go."

John's good at this. Sherlock can feel the tension he's been carrying there start to melt away under John's sure touch.

"You're massaging my earlobes with your thumb and forefinger." Sherlock just manages to keep his voice steady. There appear to be nerves that run directly from his ears to his groin and they are firing on all cylinders.

John releases his ears and shifts forward for better purchase.

"Now you're digging into my shoulders and trapezius with your knuckles, reaching deep tissue, and working inward."

John is ruthlessly seeking and destroying all of the knots Sherlock hadn't known were there, and it hurts, but in the best of ways. Sherlock leans into the pain as they dissolve under John's onslaught.

"You're easing up. You've poured more oil in the centre of my back and you're running your fingers very slowly down my spine to the top of my buttocks." Sherlock sighs involuntarily as a shiver of pleasure runs along the path traced by John's hands. "Now you're smiling at my reaction; your knees are squeezing me noticeably tighter and your pulse is elevated."

 _Stripped of other distractions, Sherlock can acutely feel the blood pumping through John's femoral arteries against the thin skin of his hips, the heat coming from between John's legs and seeping into the small of his back, the weight of John's fullness pressing down on him..._

He feels his own arousal surge as John shifts again.

"You're sliding up my torso, leaning over and rubbing your chest on my back. Your teeth are on the nape of my neck as your hands are rubbing up and down my arms. Your erection is touching the base of my spine and your legs are lined up with mine."

John's nipping at the spot under his hair where Sherlock's skull attaches to his spinal column, and it drives him to distraction as always, making his whole upper body tingle. John is draped over him completely and the spot where his cock is digging into Sherlock's skin is hot like a flesh wound.

"You're slipping down now, running your whole body over mine, hands following." Sherlock's voice catches and goes up half an octave. "Now you're kneeling between my legs and rubbing my buttocks and the backs of my thighs with more oil."

 _John is kneading his arse with both hands, deeply, sliding them into his cleft and spreading him apart while massaging until Sherlock is breathless with the stimulation, electrified, John teases then, moving down to work on Sherlock's thighs, skirting but not quite touching between his legs, tormenting him gleefully..._

"You're..." Sherlock begins, but chokes. He's lost his words and shakes his head mutely. John chuckles, rubbing his thumbs in agonizing little circles on Sherlock's inner thighs for a few more seconds before dragging him over onto his back.

John climbs onto him again, aligning their hips so his hardness is pressed tantalisingly against Sherlock's, his oiled chest slick on Sherlock's own. The top of his head is right under Sherlock's nose.

"John," he gasps.

"Yes?" John asks, running his tongue along the line of Sherlock's jaw, flicking up behind his ear before moving down to suck gently on his throat.

Sherlock plunges his face into John's hair and breathes him in. "You smell of... palm trees and hot sun and lust and herbal soap..." he manages.

John makes a pleased sound and puts his hands to Sherlock's collarbones, playing them like a piano. Sherlock moans freely, and John holds something to his lips.

"Touch, hearing, and smell all seem to be in order. What about taste?"

Sherlock opens his mouth and licks. It's the inside of John's wrist. He laps at it and then cranes his neck to follow all along the inside of John's arm to his axilla, raising gooseflesh under his mouth as he goes. "Salt... curry from dinner... coconuts... antiperspirant... sweat... copper... nutmeg."

He twists his tongue into the hair under John's arm unabashedly, and then lets his head fall back to the pillow. "Mostly, you taste of John Watson."

Sherlock's caught unprepared the swiftness and strength of John's kiss, crashing into his lips, teeth nearly colliding, thrusting his tongue fiercely down Sherlock's throat before Sherlock can even respond, as if John is suddenly trying to climb inside of him.

 _All the languid slowness, the teasing, is gone from him now, John_ wants _, every cell in his body is demanding answer, there's no softness in him anymore, everything is hard, rigid, focused, coiled to strike like an Indian cobra, it rouses Sherlock from his docile state..._

Sherlock wraps his arms around John, crushing him to his chest, and throws a long leg over John's thighs to keep him close. He intends to roll them both over so he is on top of John, but he pushes too hard and they are both still coated in oil. They roll one and half times and then John slips out of Sherlock's grasp and off the side of the bad, crashing to the floor.

Sherlock listens for John's breathing and, before he can get up or say anything, Sherlock pounces on him, barely managing to hold on to the greased body as he pins John to the carpet, face up. John growls happily and bites at Sherlock's wrists without any real force behind it. He presses his hips up, rubbing his thickness against Sherlock's stomach. He's trying to goad Sherlock into action and it's working.

Sherlock releases one of John's hands so he can snake one of his own between John's legs. There's more than enough oil for lubrication, and he slips a finger inside of John without warning, feeling his friend clench and relax around him as Sherlock rubs a thumb just behind his testes. John wraps his free hand around the back of Sherlock's neck and pulls his face closer. "Don't stop," he grunts, panting like a wild thing, his breath savoury and warm in Sherlock's nostrils.

In response, Sherlock slides another finger into him, searching for his prostate while still smearing his thumb across John's sensitive perineum. John cries out when Sherlock brushes against the gland. He frees his legs and throws them over Sherlock's shoulders, tilting his hips up, inviting Sherlock in.

Feeling John's readiness, he withdraws his fingers, steadying himself on the ground, and pushes into John. He sinks in slowly, deeply, John's body welcoming him. John's legs tighten behind his neck, shifting and letting him in that tiny bit more, fitting to him perfectly. Sherlock stills, relishing the moment of intimacy, of wholeness.

 _The smell of John's passion, sex and sweat and desire mingling in the air, the furnace of John's body threatening to burn him up, the strength of muscular thighs against his chest, tight internal muscles holding him securely, pulsing around him, the sound of John's ragged breathing, containing just a hint of a whimper, the taste of his mouth still coating Sherlock's tongue..._

John makes a stuttering intake of breath. "Sherlock..." he rasps. "Move."

Sherlock moves and John moves with him, letting him slide out and then drawing him back in, anything but passive. He keeps one hand on John's hip, feeling him undulate beneath it, and wraps the other around John's cock, stroking the smooth, taut length of it in a steady, matching rhythm.

 _John is usually quiet, given to soft, restrained noises, made only when he cannot hold them in anymore, to whispered words, if any, and the occasional deep cry of pleasure at climax, signaling Sherlock has gone above and beyond, but now he is vocal, grunting as Sherlock thrusts deeper, harder, keening at the touch of his hands, gasping audibly for breath, maybe it's on purpose, giving Sherlock aural stimulation to replace the visual, either way every sound seems to reach deep inside him, sets his heart racing ever faster, fans the flames of his desire..._

The pressure starts to build within him, ready to overflow and he doesn't try to stop it. His mind is past thinking, pure bliss racing through his synapses, shorting out dendrites, silencing neurons, demanding his full attention. He arches his pelvis forward, holding John tight to him, and lets it crash through him and into his friend, like falling, like drowning, and then the relief of catching hold of something that saves you. A harsh, guttural noise escapes his lips as he spasms within John, finally stilling and coming back to himself.

Sherlock resumes his stroking of John, keeping him where he is, wanting to feel John's orgasm from the inside. He wishes he could see John's face right now, see the brilliance around him that must be like a thousand lighthouses. He resents this loss, even as he appreciates the new facets of the experience. He satisfies himself with John's unguarded sounds of passion, with smelling his musk, now overpowering, and with feeling John's every move; the tense vibration under Sherlock's hand, the contraction within him, the pulse of his testes against Sherlock's loins.

He feels it start deep in John's abdomen, quivering around him, almost too much for his current sensitivity but he doesn't care, he delights in the too-strong sensation as it spreads through John's whole body. John is quaking with anticipation, and a few more long strokes from Sherlock are all it takes before he jerks sharply upward and calls Sherlock's name almost in desperation. Sherlock holds him tightly as he finishes, finally feeling John's warmth spill over onto his hand even as every fiber of his being softens.

Sherlock releases him and they slowly separate, as if reluctant to return to being different people. Sherlock is breathing fast and John is gulping deep lungfuls of air. He grabs Sherlock's hand and entwines their fingers, pulling Sherlock down to the floor with him. Sherlock puts his hand on John's chest to feel the rise and fall of it as John struggles to get his wind back.

 _Sherlock still marvels, even after all these months, that John wants him so unwaveringly, even now, blinded and hobbled, that he will give himself so fully to Sherlock in every way, John never shies away in fear or revulsion, never shames him, accepts his deepest desires, pursues him, lets Sherlock penetrate and dominate and own him, trusts him with life and body and soul, no one has ever done so even a fraction of the amount John does, and Sherlock could never trust anyone else enough to let them close enough to try._

John's breathing normalises at last, and he kisses Sherlock's cheek almost sweetly.

"That was... a good idea." Sherlock tells him roughly, still overwhelmed as he often is after they are together. The combination of the physical sensation on his already hyperaware nervous system and the flood and exchange of emotions that he doesn't understand but knows are important often leaves him next to speechless for minutes or hours.

"I think so, yes," John agrees and falls silent, knowing Sherlock needs to process for a while, contentedly laying still beside him.

Sherlock lets his mind do as it will, filing the memories and feelings one by one until everything makes sense again and the daze recedes. He realises he is on the floor, covered in oil and bodily fluids and is starting to become cold. The creeping sensation of discomfort, disgust, and panic starts at his feet and spreads upward, raising all the hairs on his body.

John reads his mind, or at least his sudden tension, and announces, "I don't know about you but I think a shower is definitely called for." He scrambles to his feet. "Coming?"

Sherlock lets John take his hand and pull him up, and lead him to the bathroom. Already he's starting to feel impatience, and dread, over his situation and the uncertainty of the cause, but for John's sake he shoves it to the back of his mind and tries to keep a tight hold on what they've just shared.


	4. Chapter 4

The day passes in the agonising slowness of waiting. John spends some of it sleeping, trying to make up for the lost night, but Sherlock can't rest. He paces, between the window and the kitchen table, over and over and over again, counting his steps each time, then counting the number of trips, twisting his fingers into knots as he goes.

He's still at it when John wakes, and even John's hand on his arm is barely enough to slow him in his circuit. John lets him go, biting back his protests. Doubtless he understands this behaviour is a substitute for more destructive means of coping. At last, later in the evening than Sherlock would prefer, the phone rings and he is freed.

They rush to Bart's where a package and two soldiers are waiting for them. Two large soldiers; Sherlock can feel their hulking presences tower over even him before they speak.

"Yes, yes, Official Secrets," he snaps, scrawling a signature on the proffered clipboard without bothering to ascertain whether he is anywhere near the dotted line. "Now, run along back to daddy, we've got work to do."

It's very likely only the diplomatic intervention of John that prevents them from doing something nasty to him, but he hardly gives it a thought. That's what John's for, isn't it? Either way, they eventually piss off, with a stern parting warning that Sherlock barely notices.

 _This is the difficult part, he can hardly have anyone else involved in the analysis, but John's no chemist and Sherlock can't use the equipment, he'll have to direct John, thank God Molly's not here, she'd trip them up in her eagerness to be useful, best off just the two of them, really, even though it will be slow going…_

"John," he says sharply, interrupting the doctor from whatever he's been babbling about – probably something on how he shouldn't make enemies in Special Forces. "Can you do as I say?"

"I think so," John agrees. "But really wouldn't it be better if we got someone in who—"

"No. Now, first I need you to read me the data sheet that came with the sample."

John does so, haltingly. Sherlock lets his mind go to the pristine laboratory he's created inside it for this purpose, building a model of the drug atom by atom and chain by chain, a super-scaled three dimensional molecule in his head.

 _It's clever, so clever, an organophosphate base with bromides linking rings he recognizes from virtually every common psychoactive drug known to man, LSD, THC, MDMA, he can see exactly how it would slot into the fear receptors, how it would trigger the adrenaline spike, work its way subtly into nearly every part of brain to produce complex and vivid hallucinations, paranoia, a complex molecule but so simple really and when delivered via aerosol nearly impossible to combat…_

"Got it," he tells John abruptly. He can imagine the faintly puzzled look John must be giving him now, unaware of how clearly Sherlock can visualize the string of chemicals he's just read off.

"Great," John says slowly. "Problem, though. I might be wrong, but I've got your blood tests right here and there doesn't seem to be any sign of this is in your bloodstream. Maybe it's not the Hound drug after all."

Sherlock frowns. He'd hoped it would be that simple. Then again, if it had just been the drug in its raw form effecting him, the effects should have been diminishing over time, not like this strange, belated blindness.

"No, I know we're on the track, if only I could see, I could work it out, I know it!" Sherlock slams his hand down on the bench in frustration. "It must have to do with how I metabolised it."

He makes John take more blood, and gives him a list of all the possible metabolites he can think of to screen for. Then he has John run tests on the compound itself, solubility, toxicity, reactivity to other chemicals Sherlock might have been exposed to. It takes four time as long as it should, Sherlock using his mental lab to guide John in what to do and John, clumsily, obeying.

Nine hours into it, and they are no closer than when they've begun.

"That should have formed a precipitate," Sherlock continues relentlessly. "A white one. Did it?"

John sighs tiredly. "Yes, it did."

"Good! Now add ten millilitres of potassium chloride to the solution." Sherlock hears drops go into the beaker. "Well? It should be blue. Is it blue?"

"No, it just turned cloudy," John answers.

"Damn!" Sherlock snaps. "Are you sure you didn't use potassium bromide instead? Because that could—"

"Sherlock, I can read," John growls at him. "Look, I can't keep this pace up much longer, particularly since I don't understand what the hell it is I'm doing. Have you learned anything at all from all this?

 _He's learned that if it is the Hound drug in some transformed state that's cost him his sight, it's not going to be easily neutralized by any of the fifty simpler measures he can think of, and that it's not likely to run its course without intervention, whatever its done to him won't fade away, it's going to require some kind of active reversal, and it's not going to be easy…_

"Some. Not enough." Sherlock admits.

"And you still feel like this has to be the cause?" John asks.

Sherlock nods. "It's the only scenario that fits all the data. Even if all the data doesn't quite fit it yet."

"Good enough for me." John comes over to him and slips an arm around his waist. No one's around and it's comforting to feel him physically again after hours of shouting commands, so Sherlock doesn't protest. "Look, why don't we try and get some rest and have at it again tomorrow. The new labs will be back, maybe that will give you a direction to look in, and if nothing else, we'll both be fresher. Okay?"

Sherlock agrees unhappily.

 _If it were just him, he could stay there for days without food or rest testing reactions and eliminating theories until it was solved, but working like this is exhausting for both of them, it slows his thinking to have to go through another person, to have to verbalise, he can't just connect and follow instinct, John is compliant but he can only be pushed so far, Sherlock's worn him out but there's no other way to do it…_

They decide to walk home, even Sherlock agreeing the fresh air will do him good. To his mild surprise it's morning rush hour – they'd been in the lab all night. He's bad enough at keeping track of time, of days, during a case, but now he feels complete unharnessed from any sense of the world's rhythms, without even light cues to remind him what's passing.

Sherlock stays close to John in the busy street, holding John's belt under his coat in a way he hopes is unnoticeable to passersby. He had thought they'd be strolling deserted streets in the middle of the night and he could let his guard down, not jostled this way and that by unknown masses. Crowds are bad enough when he can see them coming but now he feels like he's being attacked from all sides.

 _Anyone could be around him, he'd never know, never see a man walking straight up to him with a knife, never know if Moriarty passed within inches from him, if John slipped away from him Sherlock might never find him again, he hates this train of thought but he feels the panic starting to rise again with thousands upon thousands of people surrounding him and no way to filter out what's going on…_

Suddenly there a loud noise in his left ear and a spray of wetness on the side of his face. Already wired, Sherlock jumps practically out of his skin and turns to the source, ready to defend himself.

"Terribly sorry," a young man's scared voice mutters as it flees behind him. Someone had coughed on him while they were waiting at a street crossing. That's all it was.

"Christ," John says at his overreaction. "That's it. We're getting a taxi the rest of the way."

Sherlock doesn't bother to protest, letting John lead him to the kerb as he attempts to calm his heart, and wipe the phlegm and saliva off his skin. When they get home he goes straight into the shower, hoping to wash away the unpleasant sensation as well as the terror that had been clutching at him in the street.

He does feel calmer when he emerges, though still unsettled by how easily he had lost his equilibrium. John is concerned too, sitting beside him on the sofa and leaning into his side, the pressure of his body warm and reassuring.

"Sherlock," John says, squeezing Sherlock's thigh through the satin of his – he hopes – red dressing grown. "We're going to solve this. We are. I promise. But after today, we both know it might take a while. I think you need to figure out how to function… like this. Because you might have to."

Sherlock opens his mouth to lash out, but then shuts it. John's right, he realises. He can't be constantly on the edge of losing it. He's got to learn to work around this, he's got to find ways to be himself, to do what he needs to, without his vision. If only temporarily.

He nods silently, and John apparently sees what he needs to know that Sherlock's accepted what he's said. "I need sleep, I can't think straight. You should join me."

"Not yet," Sherlock says. He needs to think about this. "Soon."

John leaves him, reluctantly.

 _Can he still be Sherlock Holmes like this, maybe he can, as John showed him yesterday the loss of one sense is the heightening of others, there's nothing that can truly replace visual input, but he can sharpen his other senses, even in the crowd today, if he hadn't been so consumed by his own vulnerability, there were rhythms of footsteps around him, sounds of breathing, shifting, conversation to be aware of, smells of perfume and cologne and exhaust and food from shops, vibrations of the street, alternating warmth and coolness of shadows and light that could have told him as much about his surroundings as his sight could have had he bothered to tune into them, he just has to banish that amputated-limb feeling and engage his mind, he's a poor genius if he can't overrule his irrationality enough to use what he has…_

Keeping his eyes closed, as that feels more natural, Sherlock takes himself back from the moment they left the hospital, retracing their journey on the street but this time paying attention to all the cues he'd ignored before. To his surprise, he finds he can draw up a mental picture of the path they took, the streets they'd crossed, even some of the people they'd walked by – a woman in heels pushing an infant in a pram, an Indian businessman on his mobile speaking angrily, a group of school children with two harried teachers and three – no four – parental chaperones on a field trip.

Sherlock feels himself relax, slowly. It was only the darkness in his own mind preventing him from observing. He had let it wrest control from him, but he wouldn't repeat that mistake. Satisfied and relieved he turns his attention back to the cat burglar case, and it's only a matter of minutes before the answer comes to him.

"John. John, wake up!" John grunts and pushes Sherlock away.

"What? I've only been sleeping… an hour? Bloody hell."

"I know why our thief is obsessed with the pictures!" Sherlock crows gleefully. "And how to trap him."

He feels John struggle into a sitting position. "If you must."

"He only steals the jewellery to pay the bills. He doesn't get a thrill from it, or from the break-in itself. That's where we've been wrong. That's just money, he can't be trapped by luring him with trinkets, however valuable. He's got self-control there. What thrills him is the pictures – he steals personal family photos that only have value to the owners. And only ones that don't have copies or negatives or exist in digital form. He gets off on stealing memories that can never be replaced."

Sherlock is aware of how smug he looks at the moment as John breathes, "That twisted bastard. You're right!"

"Of course I am," Sherlock informs him. "Now, call Lestrade and tell him all he has to do to catch him is to have someone with a collection of historical family photos advertise for help in digitizing their collection. Our thief won't be able to resist getting to them first!"

"Glad you're back to your old self," John mutters sarcastically, though his relief is palpable. "Now if I do this will you please let me get some rest? And get some yourself? I swear you're going to turn me nocturnal."

Sherlock agrees and once everything is settled with the Yard, willingly lies down with John. He drifts off much faster than he thought he could, untroubled by the bright light that must be filtering through the curtains.

He's not sure how much later he wakes, but John's no longer beside him. He shakes off the disorientating darkness more quickly this time, but something else is wrong. He can't quite pinpoint it, so he calls out to John.

No sound comes out of his mouth. He tries again, but nothing. There is only silence. Not just from himself, but from everything around him.

 _He's being suffocated, being drowned, darkness and silence, is he dead, is this hell, he can move but he can't speak, can't hear, can't see, it feels like a vacuum, there's not enough air…_

Sherlock fumbles blindly around him, feeling like the world is spinning, like he's plunging into an unseen abyss. He falls to the hard floor, hitting it with his knees, dizzy and still screaming soundlessly for John.


	5. Chapter 5

Sherlock slams face first in to the hardwood, like his strings have been cut. His chest constricts and waves of nausea crash over him.

 _Spinning out of control, an astronaut flung from his ship, not weightless but not obeying any laws of gravity he's familiar with, the darkness lurches and flips around in his head, or he does around in it, like he's walking down a lightless hallway that keeps rotating, and so quiet, quiet like death, like the universe before the universe was, like he's the only thing in all of existence, or maybe he doesn't exist at all anymore…_

Distantly, he recognises that he is being touched, but he barely feels it. His skin is numbed, his body a shell with no connection to his self any longer. His self is reeling off into the void. The only thing that registers is the floor beneath him, or is it a ceiling or a wall or perhaps just an untethered board tumbling through space with him.

Sherlock's body's reflexes take over then, making him lift himself up enough to vomit without drowning himself in it. He feels hands on him again - John's hands, his brain tells him vaguely - but it doesn't mean anything to him. John, the person, is remote from him, an abstract, without a way to experience him. He exists now only as the plane where his skin meets Sherlock's, two dimensional and mute, lacking any frame of reference. There's no comfort there, no depth, no substance.

Sherlock shakes and tilts his head violently, trying to make a sound, trying to find an angle to orient to, any noise, any sense of direction. Slowly he realises that there is a rhythm in the dark. Something pressing on him, tapping.

 _Not a sound, a feeling, it won't stop, what fresh torment is this, poking at him, unceasing, on the inside of his wrist, getting stronger getting faster, activating his nerves, taking them from almost insensible to blazing stabs of not-quite-pain, raw stimulus, the only stimulus, and there's a pattern, repeating, zero/one, on/off, fast/slow, long/short, he knows it, if only he can remember what it is, point point point pause point point point point pause point pause point line point pause point line point point pause line line line pause line point line point pause line point line pause point point line line point point, and again…_

S-H-E-R-L-O-C-K-? S-H-E-R-L-O-C-K-?

He jumps when his brain forms it into a word at last. Morse code. John is speaking to him in Morse code. In an instant he snaps back to his body, jarringly returned to all his remaining senses. He fills his lungs with air. He can feel John's fingers on him and can again imagine the man behind them. He can feel _John_ , and smell him, and smell his own sick, taste it on his tongue. He exists once more. The world exists, though it is greatly diminished.

Pain radiates from various parts of him where he hit the floor. Everything is still silent and dark, his head still spins and his stomach still turns, and fear is rooted in in his mind, but he's a person again. At least he thinks so. He's Sherlock Holmes, isn't he? And John Watson is with him. Frantically trying to speak to him.

SHERLOCK? SHERLOCK CAN YOU UNDERSTAND THIS?

Sherlock licks his lips and says dryly, "Yes." Thinks he says. Has any sound come out of his mouth?

YOU CAN'T HEAR CAN YOU?

Sherlock hopes he replies calmly. "No, John. It would appear that I have lost my hearing in addition to my sight."

Instead of an immediate reply as he expects, suddenly bare arms are thrown around his torso. He feels the stubble of a cheek against his, hot breath on one of his useless ears. John is holding him very tightly, and John is trembling although he seems to be trying not show it. Sherlock feels John's fingers on the nape of his neck, tapping again, fast but lightly, like a whisper.

I'M SO SORRY. SO SORRY. WE'LL FIX THIS. I PROMISE.

Sherlock inhales and smells John's hair, John's shampoo in his nostrils. The realness of him helps. Sherlock still feels disconnected, disoriented, but John is a locus point. It's something. He feels John swallow against him, and there's a slight sensation of moisture on his face. It's too much for Sherlock then, and he extricates himself from the embrace.

"Am I speaking normally?" he asks, attempting to sit up straight. It's difficult, his balance is all wrong, but he can manage.

BIT LOUD, John answers, back to his wrist now.

Sherlock modulates. "Better?"

John seems to have composed himself, which is more than Sherlock can claim. He had thought blindness alone had made him helpless but that was blissful independence compared to the state in which he now finds himself.

 _So completely shut inside, taste and touch and smell all work but they can't make up for it, not even close, he's lost his agency, he waits in the dark for what will happen, he's a reactive creature now, his other senses poor and underdeveloped comparatively, even his keen sense of smell, you can't read a book with your nose however good it is, can't hear music with your tongue, can't read John's aura with your hands, whatever else they might do, he can feel his way around the flat still but with vertigo it won't stop him from ending up on the floor again, even his sense of space and direction betraying him now…_

John helps Sherlock to get up and sit on the bed, and examines him once again. As much as he can, he keeps his fingers dancing over Sherlock's skin, telling him everything he's doing and why, and Sherlock is grateful for the input, any input, any connection to the world and to John. John is quick with his cipher, surprisingly quick, the words pop up in Sherlock's mind almost like a text. It helps to imagine them that way, on a screen in his brain, and pretend that they're talking over text and everything is normal.

When John is done, his news doesn't surprise Sherlock.

PHYSIOLOGICALLY THERE STILL ISN'T ANYTHING WRONG. YOUR HEART RATE IS ELEVATED AND YOUR BLOOD PRESSURE, BUT THAT'S TO BE EXPECTED AFTER YOUR FRIGHT. I'M SORRY.

"Stop apologising," Sherlock snaps at him. "It doesn't help."

He instantly regrets it. What if he angers John? What if John withdraws, stops speaking to him? He'd be utterly alone.

John doesn't withdraw, but Sherlock can feel his fingers tense and knows he's not entirely unaffected. He makes no comment about it, though, and chatters on about what they have to do now, going to hospital, more tests, as he helps Sherlock to the bathroom, to get cleaned up and to dress. Sherlock's sense of balance is improving, but not enough to do so many complicated tasks by feel alone.

 _He resents how much assistance he requires, but mustn't let it show, he resents how pathetically grateful he is for John's constant presence too, the stream of information, inane though most of it is, and so meagre, like surfing the internet on dial-up after you've been using fibre-optics, like an IMAX movie described in a tweet, but without it he'd have nothing, not even his lingering sanity…_

The day plays out very much as the one after he lost his sight, although managing to be both more incomprehensible and even more dull. John takes him to hospital, he has another scan, they wait for results, they find nothing wrong with his auditory centre, they find nothing wrong with his ears, they take more blood, they run more tests. And Sherlock tries not to scream with anger and frustration and hate at everything around him. It wouldn't be satisfying anyway. He couldn't hear it.

 _And John talks to him, John tells him everything he can think of, on his wrist, on the back of his hand, on his forearm, on the small of his back, on his calf while he's in the scanner, John never stops touching him, John never stops giving him data, John knows somehow without being told that if he stopped it would be like he didn't exist and maybe like Sherlock didn't exist either, and he owes John everything, and he wishes that he didn't, he wishes that there was no John with his steady hands that must be cramping by now and his unthinking devotion, because then this would all be very simple…_

The only thing close to a breakthrough comes after hours – or is it days – at the lab when his most recent blood tests come back.

THERE'S SOMETHING.

"Tell me! Quickly!" Sherlock demands.

John raps out the chemical formula in shorthand they've hurriedly devised.

NOT MUCH OF. A FEW PARTS PER BILLION. IT'S NOT A METABOLITE OF THE HOUND DRUG IS IT? THEY LOOK SIMILAR BUT IT'S OFF ISN'T IT?

Sherlock is surprised John was able to discern that much. "Yes. It shares a basic structure but there are sulphides not present in the original. And there's mercury."

MERCURY CAUSES SENSORY DISABILITIES. BUT NOT IN THESE AMOUNTS. YOU'D HAVE MORE IN YOUR SYSTEM AFTER BINGING ON SUSHI.

"And this is bound up in a complex molecule. You did test for free mercury and its simple compounds?"

ALL THE HEAVY METALS, YES. DO YOU THINK IT'S A POISON?

"Possibly," Sherlock says. "Or it could be a chance combination of unrelated toxins. There's no way to be sure unless we find more of it."

BUT NOT THE HOUND DRUG.

"No," says Sherlock, grimly. He falls silent. Talking without being able to hear is exhausting and frustrating, and this new discovery only makes him feel further away from the answer. The Hound drug has been their only lead and there's so little of this new compound in his system that either it's not actually the culprit itself but just a byproduct or, worse, it is the cause of all this and his body has already metabolised most of it. If that the case, if it's leaving his system but his symptoms are worsening, then that would mean its effects are mostly likely permanent. And quite possibly degenerative.

John thinks it too, Sherlock can tell, his hands are shaking just a bit and he starts to talk about how they should go home, get some rest, come at it tomorrow, maybe Sherlock will feel better. Sherlock barely registers his words. As soon as he thinks it, permanent, degenerative, it's the only thing in his head and he knows it to be true. He's tried so hard not to think it, to do as John's asked and stay hopeful, but he can't any longer. The words echo and grow within him.

He follows John docilely out of the hospital and on to the street, that thought choking out all other thoughts now. It's busy and it takes a little while to get a taxi. The street is strange and daunting in this state, just walking, even with John's aid, seems as treacherous as crossing the Himalayas on foot with a murderous horde at his heels.

 _He can't anticipate, he can't prepare, he can only respond, and poorly, slowly, clumsily, the smallest sensations now huge and ominous, every brush of a passerby an attack, every vibration the start of an explosion, every current of air a bullet whistling past him, every unfamiliar smell toxic gas, even when they get in the car it's not much better, every lurch and turn the prelude to a smash-up, how could he possibly persist in this state, at the mercy of everyone and everything around him, especially when there is so little mercy in the world, he doesn't even have any himself…_

Sherlock tries to hide his thoughts, his near frenzy but he knows he must be betraying his reactions to John however hard he tries to keep them under control. John's fingers feel worried and he's talking about open cases now, trying to get Sherlock to work, to deduce, to be himself. But it's not going to help this time, because he's not himself any longer. How can he possibly be Sherlock Holmes like this? How could he ever be again?

He holds it together until they reach the relative safety of the flat. But once he's inside he can't contain it any longer. He shakes John off him and lashes out, aimlessly, full of rage and despair. His fist connects with the wall and he feels the crash as the steer skull falls from its mount. His hip bangs painfully into the sharp corner of the desk and he pushes it, overturning it, before spinning around and grabbing the lamp, smashing it into another wall. His hand feels warm and wet and he realizes he must have sliced it up, but it doesn't seem to matter.

 _The darkness, the void, it's inside him and all around him, how could he think to ever escape it, because it is him and he is it, he is the darkness, how could he ever have a real life, ever be whole, ever be happy with John and clean and free and live in his light and warmth, this is his punishment for trying, he sees it now, because he's always been dark and cold, a creature like him can't live in the sun, not really, he might orbit it briefly and try to stay, a comet captured by a star's gravity, but he belongs to the void, to its freezing depths crystalising within him, and he must always return there, there's nothing more to fight, there's no more pretense, no playacting at living as others do, the void is calling to him, singing to him, and it offers the only kind of relief left, the only answer to the Final Problem which he can no longer escape and doesn't really want to…_

A hand grabs his bicep and he pushes John away again, but John's not having it. Sherlock fights, but John tackles him, knocking him to the floor and straddling his chest, holding his wrists tight above his head, pinning him.

"Let me go," Sherlock demands, struggling.

John shifts so he can keep Sherlock at bay while still being able to tap on his forearm.

NOT UNTIL YOU TELL ME WHAT IT IS YOU THINK YOU'RE DOING. I KNOW YOU'RE FRUSTRATED BUT YOU'RE ONLY GOING TO HURT YOURSELF. YOU'RE ALREADY BLEEDING.

"It doesn't matter anymore. I can't live like this."

YOU WON'T HAVE TO. WE'RE GOING TO SOLVE THIS.

"You don't believe that," Sherlock growls. "Despite your determined attempts to appear otherwise, you're not stupid. You know what's happening to me. This won't get better. It will probably get worse. This is all there is for me now."

I DON'T AGREE. BUT EVEN IF YOU'RE RIGHT THEN YOU ARE GOING TO HAVE TO LEARN TO DEAL WITH IT. DESTROYING THE FLAT, HURTING YOURSELF, IT'S NOT GOING TO HELP.

"No, it's not," Sherlock agrees, feeling suddenly very calm. "Like I said… I can't live like this. I can't work. I have nothing. I can't be me like this. You know I can't. It's best if I go now. Before it gets worse."

There is a long pause while John puts it together. Sherlock's not sure what he expects but it isn't the stinging slap to the face he gets.

 _He can feel John's anger in it, not just anger, anger is a punch, there's respect in a punch, man to man, striking with an open hand is disdain and betrayal, and that hurts more than the slap, he'd thought John would understand, at least a little, John knows him like no one's ever known him, knows he needs to work, knows he can't exist apart from the work, how can he explain to John now, about the darkness, about where he really belongs, what he really is..._

COWARD. His nails dig into Sherlock's flesh with every letter.

"John," he pleads. "You know I can't go on like this. It's cruel to ask me to."

John's released his wrists and is keeping him in place through bodyweight and sheer force of his rage, coding now on Sherlock's sternum with his whole hand, not taps but blows, reverberating through Sherlock's whole body.

YOU WANT TO SPEAK TO ME ABOUT BEING CRUEL? HOW DARE YOU? AFTER ALL WE'VE BEEN THROUGH HOW DARE YOU. YOU ALWAYS ARE IN SUCH A HURRY TO LEAVE, TO DIE, AND YOU CALL ME CRUEL. YOU LIE HERE AND TELL ME TO MY FACE THAT YOU HAVE NOTHING AND I'M THE CRUEL ONE.

"And you? You could live like this? If you couldn't work, if you had nothing else, only me, but none of the elements of the life we've made together, just endless dependence and idleness, that would be enough for you, if you were with me?"

IT DOESN'T MATTER IF IT WOULD BE ENOUGH. IT WOULD BE SOMETHING. AND I WOULDN'T GIVE UP ON US, ON YOU, ON LIFE, OVER IT. I WOULDN'T DO THAT TO YOU. WE MEAN MORE THAT.

"I'm not trying to do anything to you, you just don't understand. It would be better for you, for both of us-" Sherlock's words are cut off by John's mouth suddenly on his, hard and bitter and determined.

John breaks the kiss after long seconds but leaves his face right there; Sherlock can smell John's breath and feel spittle fleck his face as John speaks with mouth and hands at the same time. He's yelling, screaming at Sherlock, uncaring that his friend can't hear him.

DON'T YOU TELL ME WHAT'S BETTER. YOU DON'T HAVE THE RIGHT, YOU SELFISH FUCKING CUNT! YOU DON'T GET TO DECIDE WHEN YOU'RE DONE, BECAUSE YOU'RE MINE, REMEMBER? IT'S NOT UP TO YOU ANYMORE. AND I SAY YOU'RE STILL SHERLOCK FUCKING HOLMES WHETHER YOU LIKE IT OR NOT. I DON'T CARE IF YOU HAVE TO CRAWL ON YOUR HANDS AND KNEES TO THE NEXT CRIME SCENE. I DON'T CARE IF YOU HAVE TO LEARN TO SOLVE CASES BY SMELL ALONE AND BECOME THE WORLD'S ONLY BLOODY SNIFFING DETECTIVE. I DON'T CARE IF I HAVE TO STAY WITH YOU EVERY SECOND OF EVERY DAY AND BE YOUR EYES AND EARS AND YOUR GUIDE DOG AND YOUR SLAVE. YOU ARE NOT ALLOWED TO LEAVE AND YOU ARE NOT ALLOWED TO DIE AND YOU ARE NOT ALLOWED TO GIVE UP. AND IF I HAVE TO BEAT YOU BLACK AND BLUE TO CONVINCE YOU OF IT, I BLOODY WELL WILL, YOU WRETCHED, HEARTLESS ARSEHOLE.

John kisses him again, even more forcefully, and Sherlock responds despite himself, pushing back up against him, biting at John's tongue and feeling his lips bruise beneath John's. John keeps talking, his fingers to Sherlock's throat as they kiss, like he'd rather be strangling him than speaking to him.

SO IS THIS THE ONLY THING YOU UNDERSTAND? he demands, plunging his tongue down Sherlock's throat. VIOLENCE AND SEX, IS THAT THE ONLY WAY I CAN GET THROUGH TO YOU? THE ONLY WAY I CAN MAKE YOU UNDERSTAND ANYTHING, THE ONLY WAY TO GET YOU TO CARE AT ALL?

 _No, thinks Sherlock, but he's not sure it's true, he doesn't do feelings, especially not other people's, physicality translates, it always has, he can read John's heart in his body sometimes, is that synaesthesia too, emotions only registering when they come in the form of caresses or blows, in the blood and sweat and skin against his, no matter the words that are said, even now, he doesn't understand, John's right, he knows John must be right, John's usually right about these things, but he can't feel it, doesn't understand why he should stay when it will only hurt them both, when he doesn't belong, when he can only bring obliteration to what's around him, it's his nature, always has been and now it's been revealed and why doesn't John see it too..._

FINE, John says, the impact of it enough to leave a mark. IF I HAVE TO FUCK SOME SENSE INTO YOU I WILL.

John tears himself away and for a moment Sherlock thinks he's letting him up, but instead he flips Sherlock over, roughly, keeping a hand on his neck like he would a dog and holding his wrists with the other. Before Sherlock's quite registered what is happening, something is tightening around his wrists, binding them tightly behind his back. John's belt.

"John, I… you don't understand," he protests.

John shoves Sherlock's shirt halfway up his back, one hand fisted tightly in Sherlock's hair and the other gripping his waist and tapping furiously with his thumb.

YOU BET I DON'T. AND I DON'T WANT TO UNDERSTAND. BECAUSE WHATEVER IT IS INSIDE YOU THAT MAKES YOU THINK THAT ENDING YOUR LIFE IS A VIABLE SOLUTION TO THIS PROBLEM FOR EITHER OF US DOESN'T DESERVE UNDERSTANDING. IT DESERVES TO BE DESTROYED. IT DOESN'T GET TO HAVE YOU. IT DOESN'T GET TO WIN. YOU THINK I DON'T KNOW, BUT I CAN SEE IT THERE, IN YOUR EYES. YOU THINK IT'S YOU BUT IT'S NOT, IT'S LYING TO YOU AND YOU BELIEVE IT. YOU BELIEVE IT MORE THAN YOU BELIEVE ME. AND I'M NOT GOING TO PUT UP WITH IT AND I'M NOT GOING TO LET YOU GO, AND IF THIS IS THE ONLY WAY TO KEEP YOU PRESENT, THEN THAT'S WHAT I'M GOING TO DO, BECAUSE I'M OUT OF GODDAMN IDEAS.

John's unbuckling Sherlock's trousers, now, yanking them down harshly until Sherlock is exposed, arse in the air, head on the floor, completely at John's disposal. John is stronger than Sherlock is, he couldn't get away if he tried, and it sinks in for the first time that John is serious, that they have reached the point where they have run out of words for each other in a way that is more final than it's ever been and this is all John can think to do. And for a moment Sherlock feels afraid. Afraid of John, of how far he's pushed him and what he's about to do. Afraid of John's desperation and anger and fear.

 _And he doesn't want it to happen, but he does, he does more than anything, to feel something in his whole body that supersedes sight or hearing or anything else, something raw, something consuming, maybe it will be strong enough to chase away the void, to keep it from seducing him, this more brutal seduction, but John's never been like this before and it's frightening, he could stop it, couldn't he, if he wanted to, John would stop if he asked, there's a word and if he used it John would stop, wouldn't he, or is he too angry, has it gone even beyond that word, does Sherlock even want to say it, does he dare to and then find that John won't stop, or worse that John will, has he said it already, it's so hard to tell whether he's speaking, he must not have because John hasn't stopped and that's good because he almost definitely doesn't want him to, because if he stops Sherlock's brain never will, not until the darkness take what belongs to it and that's what John is trying to prevent…_

He doesn't say it. He's almost sure he doesn't. He can't fight the void and he doesn't want to fight John, but maybe John can fight it for him. Maybe John can explain everything to him.

John pushes inside him with no warning, merciless, slicked only with saliva, and it hurts but it's also like sparks going off inside his head, the closest thing to light he's had for days. And John is so warm, he'd forgotten how warm. John's heat warms him from the inside, melting away the pain. John's hand on his hip is digging into Sherlock's flesh and his other twists tighter into Sherlock's hair, as John begins to move, thrusting slowly at first, but hard and deep, as deep as he can go, like he's trying to exorcise whatever demon is within Sherlock.

And Sherlock feels John's fury and John's terror and John's devotion in every movement, he feels the abandon, that John is giving Sherlock everything, every bit of him, even now, even when John could easily lose it all, lose Sherlock and everything he's given Sherlock, still he gives more. John is claiming him this way, John is trying to hold on to him, trying to keep him here the only way he knows how. John won't let the void have him, he won't let anyone have him, not even his own fickle mind.

 _He's John's, how could he have forgotten, John saved him and keeps saving him, and the darkness has no place in him, he let it in and let it stay and that was wrong of him, how could he have thought of leaving John, he'd felt at peace when he'd first decided and now the thought of what he'd nearly done, what he'd been so sure was the thing to do, makes him feel sick, weakens him so that his knees nearly buckle under John's battering, he'd been so wrong, he'd almost ruined everything, he'd almost destroyed the only person he cares for, he can't exist without John, even non-existence without John is just as unthinkable, can he ever be forgiven, he must be, he must find a way to live, to atone, to be Sherlock-and-John again…_

And John is thrusting harder, rougher, and it's pleasure-pain together, and so fierce. It makes him ache from the inside out yet Sherlock finds himself growing hard beneath the onslaught. Every nerve is alive, all his remaining senses engaged, overloaded, and his mind finally quietens. John is still furious, but there's so much than that, and Sherlock wants to feel all of it, to understand, to take it into himself and let it scream through his veins and cleanse him of everything dark and bad inside of him. When Sherlock responds to John's savage rhythm by rutting back into him, he can feel John's relief, though he doesn't relent in the least. John lets go of his hair to wrap his hand around Sherlock's cock, leaving Sherlock's face pressed into in the rug as he fucks him within an inch of his life.

 _That's what it feels like, such utter ferocity, like John is forcing him right to the edge, forcing him to look at the abyss, off the cliff face, to see not the cool release of non-existence but the sharp rocks below, waiting to shred him and bleed him, making him face the truth so that he will never come near the edge again, so John can resurrect him and know that Sherlock really does belong only to John, not even to himself, not even to his own mind, or to anything that lies beneath it, and it's true, of course it is, he'll never let anything else have him again..._

"John," Sherlock cries as his climax builds almost against his will, hoping to be heard. "John."

John speeds up, ruthless, his hand around Sherlock like iron and his cock burning within Sherlock's thawing body. But then John he leans forward and puts his mouth to the small of Sherlock's back, using his tongue flick out the letters, wanting to make sure he's in Sherlock's head, too.

SHERLOCK, he says and it's tender and sensuous and mournful, completely at odds with his physical actions yet somehow both make sense together. MY NIGHTMARE. DON'T EVER MAKE ME WAKE UP.

"Yes, John," Sherlock whispers. "Yes, I'm yours."

 _And they plunge off the edge, together, coming as one, and Sherlock isn't sure which body is his or even where they begin or end and it's like the universe has just been reborn inside of him, the light and heat and infinite mass, and it's so bright in his head it's like daylight on Mercury, and John is his and he is John's and that's all he needs to know, and it will never be dark or cold again and he will never be alone and he will never heed the void again and he will never try to leave as long as he can be with John, as long as they have this…_

They come down like a plane crash, and John releases him, too soon, but a thousand years would be too soon. Sherlock rolls on his side, hands still bound behind him, gasping for air, all his thoughts still irradiated, his body on fire, bliss and agony mingling under his skin.

And then John is with him again, loosing his bonds. He covers Sherlock in kisses, soft ones, all over his throat and shoulders and face, winding his arms around him and talking so incredibly delicately into the soft skin behind Sherlock's ear.

SHERLOCK, SHERLOCK, I'M SORRY, I WENT TOO FAR. I SHOULDN'T HAVE DONE THAT. NOT WHEN I WAS SO ANGRY, NOT LIKE THAT. DID I HURT YOU? I WAS WRONG TO HAVE. I'M SORRY.

Sherlock lets his lips rest lightly at John's temple, unnerved by this regret. John had known what to do, and it had worked. Why does he doubt now?

"No. I was… You were right. I didn't understand. I'd got… I'd got lost. I needed you to find me. I needed you to feel for me, to show me how. I'm back now. I promise. I won't try to leave again. I never want to leave you. Not really." He butts his head gently against John's, like an apologetic kitten. "Sometimes the darkness drowns out everything else. Even when I can see and hear and worse when I can't. But I won't go back there again, I won't listen."

He feels John's curt nod, not truly understanding but accepting. I STILL SHOULDN'T HAVE. I WASN'T. I DIDN'T. John pauses, swallowing something back. IT WAS NOT GOOD OF ME.

Now Sherlock 's confused, because of course it was good, it did exactly what it was supposed to do. But he doesn't press John about it because he's suddenly distracted by the fact that it's still bright behind his eyes. It's not just the fading afterglow in his mind. He can see something. There's a shape to it, areas of brightness and darkness.

"John, move away from me a bit," he says slowly, pushing him off. John does as he's told and Sherlock tries to focus.

It's there. It's real. A halo, a photonegative, a brilliant ghost. It burns into his retinas, glowing comfortingly. He watches, fascinated, as the figure of light reaches out to touch his forearm.

WHAT IS IT? WHAT'S WRONG?

Sherlock looks into the yellow orange embers of John's face and smiles. "I see you."


	6. Chapter 6

Sherlock can sense John's disappointment when he has to clarify that his sight hasn't been fully restored, just that he can see John again, or at least a projection of John from his own mind. Still, it's a vast improvement.

SO IT'S JUST ME, NOTHING ELSE?

"So far," Sherlock admits.

WHAT DO I LOOK LIKE?

"Like... Like a cut out of yourself. But fluid. Like molten gold. I can make out your features, faintly, your expressions, when you're close."

John hauls Sherlock to his feet and Sherlock tries not to let on how stiff with pain he is. He's covered in bruises and cuts, not all of them John's doing, and he's sore inside and out. Walking normally will be a trial.

 _But he doesn't mind, the pain, the aches, the marks on him, they make him feel, they make it clear that he's alive, that he can still experience the world, they remind him John will never give up on him, no matter what it takes, and they remind him who he is..._

They do some experiments and discover that Sherlock can reliably see John's form in a radius of about four feet. He is most visible and defined when he is closest and when he is moving about and speaking. Beyond four feet he wavers in and out of existence, depending on how active he's being. Within that space if John picks something up, or puts his hand on a piece of furniture, Sherlock can see it faintly, just the bit that John is touching, as if it's illuminated by him. When John stands very still he becomes faint, but doesn't go out.

MAYBE THIS MEANS YOUR BRAIN IS REWIRING ITSELF. MAYBE IT'S LEARNING HOW TO CONVERT INPUT FROM YOUR OTHER SENSES INTO VISUAL DATA. YOU'RE "SEEING" MY BODY HEAT, VIBRATIONS OF MY MOVEMENTS, MOTION OF AIR, THAT ARE TOO SMALL FOR YOU TO PICK UP AS WHAT THEY ARE, BUT YOUR SUBCONSCIOUS IS PUTTING THEM TOGETHER FOR YOU TO MAKE A PICTURE. WE ALREADY KNOW YOUR BRAIN IS PRONE TO MIXING UP SENSORY DATA.

Sherlock considers this. "Perhaps. But why just you? And why just visual?"

The golden god that is John shrugs. YOUR MIND IS ALREADY ACCUSTOMED TO SEEING IN A WAY THAT INVOLVES OTHER SENSES, SO IT WOULD HAVE BEEN THE EASIEST CONNEXION TO MAKE. SAME WITH ME – THAT PATHWAY WAS ALREADY THERE AND NEVER REALLY HAD MUCH TO DO WITH YOUR SIGHT. MAYBE IT JUST NEEDED TO BE REACTIVATED. SEEING OTHER THINGS MIGHT FOLLOW AS YOUR BRAIN ADJUSTS. HEARING TOO. YOU MIGHT HEAL YOURSELF IN TIME.

" 'Reactived?' Is that what we're calling it now?" Sherlock asks, teasingly, feeling optimistic for the first time in days. To his surprise John doesn't retort, but shifts from foot to foot and looks at the floor.

LET'S GET YOU CLEANED UP, he says, taking Sherlock's hand. Sherlock looks down.

 _He can see his own body too, he should probably mention that to John, but it's not glowing, it's like a pencil sketch, a first draft of a cartoon, no light or colour, still it's much less disorienting being able to tell where he is in relation to John, and he'd forgot about the lamp, about his outburst, about the cut on the back of his hand that is now throbbing violently, blood smeared like charcoal, what else had he got blood on, it does need tending, he knows that much..._

He lets John lead him to the bathroom and peel off his stained and torn clothes. John starts a little when he sees the state of Sherlock's body but doesn't say anything. He fetches his bag and carefully cleans Sherlock's cuts, then takes Sherlock's hand and begins to stitch.

I'M SORRY IF THIS HURTS, IT REALLY NEEDS TO BE CLOSED, John tells him, tapping his foot against Sherlock's to keep his hands free.

Sherlock pays no mind to the pain, he's too fascinated by the information his brain is feeding him, by having something to look at in what seems like an eternity. Especially when that something is John Watson.

 _John is sewing him up, drawing the rent halves of skin back together with needle and thread, and his own two hands, for all their minor and major catastrophes John's never had to do this before, it's so intimate, more intimate than shaving, more intimate, somehow, than sex, having someone working beneath your skin, even though the wound is relatively minor it still feels like his life is John's hands, and it is, of course it is, John is always putting him back together, literally, figuratively, in all ways, doing whatever it takes just to keep him in one piece..._

WHAT? asks John, after long minutes of staring. DOES IT HURT TOO MUCH?

Sherlock shakes his head. "Not at all. It's just pleasant to be able to see you again. That's all."

John gives what appears to be a weak smile and finishes quickly.

"Thank you," Sherlock tells him. "I'm going to bathe now and then we'll go to Bart's and you can scan me again. More blood tests as well." Now that he has even this tiny portion of his senses back, he's hopeful again, certain that they can find a cure or at least a cause. He feels motivated, invigorated. It feels good.

John agrees that they should definitely retest everything after this new development but points out a flaw in his plan.

IT'S TWO AM, SHERLOCK. WE CAN'T JUST SPONTANEOUSLY POP IN FOR A QUICK ONE. NO ONE WHO CAN HELP US WILL BE THERE. I'LL SEND A MESSAGE TO MOLLY AND CAROLINE AND WE'LL SET SOMETHING UP FOR FIRST THING IN THE MORNING. OK?

Sherlock agrees, a bit deflated, but knows John's right. John turns to leave the bathroom but Sherlock stops him. "No. If you go, everything will be dark. Shower with me. You need one anyway."

John demurs, which is strange because showering together is one of his favourite things, but he consents to stay in the room. He's still and quiet, obviously thinking about something, but Sherlock can still make out his comforting glow through the shower curtain, even if it is dimmed. To add to the strangeness, once Sherlock is clean, he immediately finds that he's exhausted while John insists he's not tired. Sherlock flags this additionally as extremely odd, but is too worn out to ponder it and ends up collapsing on the sofa, dead to the world in mere minutes while John sits up and reads, still near enough to be seen. His embers warm Sherlock's mind as he sleeps.

When Sherlock wakes John is no longer in range, but has covered him with a blanket and is, by the smell of things, making Sherlock's favourite blend of coffee. Sherlock fumbles his way to the kitchen until he's close enough to perceive his friend, who presses a steaming mug on him. Sherlock wraps both hands around it and perches on one of the chairs, blanket still around his shoulders.

 _Something's wrong, he's sure of it now, John is quiet, too quiet, some of that can be excused by the fact that Sherlock no longer needs his constant stream of consciousness in order to know anything at all, but it's more than that, he's distant, touching Sherlock only when he has to relay something, hovering at the edge of Sherlock's ability to see him, where his expressions and emotions are nearly impossible to detect, even his light is wrong, less golden than tarnished bronze, has Sherlock done something wrong, has something happened and John doesn't want him to know..._

"John." Sherlock says and John reluctantly comes sits across from him, obediently placing fingers on his wrist. "Have I missed something?"

Sherlock can feel the sigh in John's body. There is a long pause.

SHERLOCK. WHAT I DID YESTERDAY. THE PERSON THAT I WAS YESTERDAY. IT WASN'T OKAY. IT SCARED ME. I DON'T EVER WANT TO BE THAT PERSON AGAIN.

Sherlock is even more bewildered now but decides to address what has been presented to him. "You won't have to be. I'm better now. You fixed me."

John shakes his head, violently. IT WASN'T OKAY. I'M GLAD IT CAME OUT RIGHT, THAT YOU'RE DOING BETTER AND NOT. NOT LIKE YOU WERE. BUT THAT DOESN'T MEAN WHAT I DID WAS RIGHT. I DIDN'T ASK, I JUST TOOK.

"When have either of us had to ask? We belong to each other. Don't be stupid. Besides, we have the word, remember? You insisted we have it. I could have said it, but I didn't. I could have tried to stop you, really tried, but I didn't. It– you– were what I needed, even if I didn't know it right away. It's fine, John. It's good."

IT'S NOT FINE, John retorts and if Sherlock could hear him he knows it would be a snap. AND IT'S CERTAINLY NOT GOOD. NOT SAYING NO ISN'T THE SAME AS SAYING YES. WHEN THINGS ARE GOOD, WHEN WE'RE BOTH INTO IT, WHEN WE BOTH KNOW WE'RE PLAYING, THAT'S ONE THING. THAT'S NOT WHAT THIS WAS. I WAS SO SO ANGRY WITH YOU. I WAS FURIOUS. WHAT YOU WANTED DIDN'T MATTER TO ME. AND YOU WERE INJURED, SUICIDALLY DEPRESSED, AND DISABLED, IN NO SHAPE TO DEFEND YOURSELF AND NOT THINKING CLEARLY. I VIOLATED–

Sherlock starts before John can finish, bridling at this. "You didn't violate me. Don't use your misplaced guilt to tell me I'm not capable of making it clear when I want something to stop. Or that I don't know my own mind. If I tell you that it was good for me, it was."

BUT I HAD NO WAY TO KNOW THAT AT THE TIME! YOU COULD HAVE BEEN HATING ME FOR EVERY SECOND OF THAT AND I WOULDN'T HAVE KNOWN. I DIDN'T WANT TO KNOW. I WASN'T IN CONTROL.

Sherlock finally starts to understands why John is so upset, even if he still finds the reasoning ridiculous. He tries to be gentler. "You would have known, because you know me. Even when you're angry and you don't think you care, you do. You still know me and know what I need. Does it matter if it's sometimes for the wrong reasons? And if I'd wanted you to, really wanted you to, if I'd said the word, you would have stopped."

WOULD I THOUGH? I KEEP ASKING MYSELF THAT AND I DON'T LIKE THE ANSWER I GET. I'M AFRAID OF THE MAN I WAS YESTERDAY. AND YOU SHOULD BE TOO.

"You would have," Sherlock insists. "I know it."

HOW?

He takes John's hand and puts it to his lips. "Because I know you. You're John Watson. And I'm Sherlock Holmes."

I THINK WE BOTH FORGOT THAT YESTERDAY.

Sherlock nods. "But that doesn't mean it wasn't still true."

IT ALSO DOESN'T MAKE THE THINGS I DID RIGHT. EVEN IF THEY JUST HAPPENED TO WORK OUT.

"They didn't just happen. You knew. Even if you didn't know you knew. You didn't hurt me."

 _Not in any way that mattered, John hasn't hurt him, but it feels like John had somehow hurt John, and he doesn't understand how that's possible, can something have been right for Sherlock and wrong for John at the same time, morality is confusing at the best of times, and this feels like completely new territory, he would just ask John to explain it to him but John seems to be having his own difficulties with it..._

I'M GLAD I DIDN'T HURT YOU. BUT I STILL DON'T FEEL RIGHT ABOUT IT. I GOT A GLIMPSE OF SOMEONE INSIDE ME THAT I DON'T LIKE. THAT'S SOMETHING I JUST HAVE TO DEAL WITH I SUPPOSE.

"Well do it quickly, John, you're no good to me like this." Surprisingly, this seems to help, jarring John from his painful introspection.

John nods curtly and his fingers twitch like he's going to say something but he doesn't. He settles back in his chair and they drink their coffee in silence. John seems to relax and by the time they reach Bart's yet again he seems almost back to his usual self.

This time they take the scan with John first out of view and then where Sherlock can see him, to compare his brain pattern when he's "seeing" and not.

I'VE ALWAYS WONDERED WHAT WAS GOING ON IN YOUR BRAIN WHEN YOU SEE ME GLOW, John comments as they both put street clothes back on. ALTHOUGH I SUPPOSED IN THIS CASE THERE MIGHT BE SOME CONFOUNDING FACTORS.

"You can scan my brain whenever you like," Sherlock says earnestly and John gets gratifyingly brighter, like turning up a kerosene lantern. Unfortunately Caroline can't review the results until a little later and Sherlock doesn't want any one else seeing them. "Bad enough she has to," he grumbles and John ignores it.

LET'S GET BACK. SHE'LL CALL AS SOON AS SHE'S REVIEWED THEM. MIGHT BE TRICKY GETTING A TAXI THIS TIME OF MORNING THOUGH.

Sherlock shakes his head. "Let's get breakfast first. And then take the Tube."

THE TUBE? John asks, uncomprehending. BREAKFAST?

 _Even though the new partial sight might be the key to a cure or the beginning of recovery, he can't get his hopes up too much, he can't put everything on hold waiting to find out, he's got work, he's got to figure out how to live like this, he can't fall back into despair, if only for John's sake, he can't do that to John again, can't force him into that position again, he's got to act like this is permanent and figure out how to work around it, that's what Sherlock Holmes does and he can't stop being Sherlock Holmes again even for a second..._

They find breakfast in the form of greasy egg sandwiches at a cafe not too far from the hospital. On the way Sherlock practices using John as a guide to navigating the street traffic, and judging air currents and paving stone vibrations to determine the distance and number of other pedestrians.

"Four people. Passing us," he tells John.

FIVE. BUT YES. John's caught on quickly.

"There's a bus on the street. Ahead of us." He can smell that one, and felt the warm gust of air as it stopped.

WHICH SIDE OF THE STREET? John demands.

"Near side," Sherlock smirks. Easy.

WHICH IS WHAT?

Sherlock quickly reviews the turns they've take. He's pretty certain they went out the main doors of Bart's. "North. The north side of the street. We're walking east towards... Noble Street." He's less confident this time, but John squeezes his fingers, pleased.

EAST SOUTHEAST, BUT CLOSE ENOUGH. PERHAPS I SHOULD START ASKING FOR ANSWERS IN DEGREES.

Sherlock smiles privately at that as they reach the cafe and sit down. John's not going to give him any slack now, which is as it should be. After they eat John makes him give the route to the nearest tube station before they set out.

 _He's getting better, he can feel it, the information is there, it's just a matter of learning to apply it in new ways, to listen to his other senses and not let them be weak anymore, he can feel his mind palace reconfiguring inside his head to suit these new needs, maybe his brain will start converting that data in sight or even sound someday, like with John, but John's special and he can't count on that, has to make do with what he's got, he kind of likes it now, he can pretend it's a game, it's certainly challenging and so few things are..._

It's surprising how exhausting thinking like this is, though. It requires all of his focus to interpret what's going on around him, and most of his energy. Eventually it will become second nature but now it's all consuming, leaving no room for anything else. He's almost relieved when they get on the crowded, standing-room only tube carriage. The press of people is unsettling, but at least he's stationary and so are they, so it's easier to deduce individuals, and almost relaxing after trying to keep himself oriented on the street.

 _Female on his left, her body spray says young adult, she has a dog, is listening to music judging by the way her to is tapping, male behind him, tall, taller than he but only just, halitosis, the part of his suit that brushes Sherlock is wrinkled but he's carrying a briefcase, late for work after a night out..._

It's not as much as he could get with his full senses, but even having to have a raw sketch of those around him make everything a little less intimidating. And of course he has John, his beacon, right in the center.

HANG ON PHONE John taps into his hand and fishes his mobile out of his pocket. Sherlock can't make out what he's saying but he turns animated and his brightness increases and changes colours, going from yellow to red to a low burnt orange.

"What? What is it?" Sherlock demands before he's even hung up.

John steps close to him, close than he would ever normally be in public, practically within the folds of Sherlock's coat.

CAROLINE FOUND SOMETHING. SOMETHING WE'D ALL BEEN MISSING.

"Well?" hisses Sherlock in a low whisper.

REMEMBER EVERY TIME WE TOOK A SCAN, YOUR AUDITORY AND VISUAL CENTRES SEEM TO BE WORKING NORMALLY, OVERACTIVE EVEN? WELL THAT WAS THE CASE THIS TIME TOO, EXCEPT THAT WHEN YOU SAW ME, CERTAIN ACTIVITY IN YOUR FRONTAL AND TEMPORAL LOBES DROPPED OFF, AND ACTIVITY IN YOUR VISUAL CORTEX DECREASED SLIGHTLY TOO.

"Dropped off? Why?"

John shakes his head. IN ALL THE OTHER SCANS YOU SHOWED EXTREME ACTIVITY IN THOSE AREAS, BUT WE THOUGHT THAT WAS JUST NORMAL FOR YOU. YOU'RE ALWAYS THINKING, VISUALISING, IMAGINING. I'D EXPECT YOUR SCANS TO BE OVERACTIVE IN THOSE AREAS. BUT IF THE ACTIVITY DECREASES WHEN YOU ARE CONFRONTED WITH SOMETHING YOU CAN ACTUALLY SEE... SHERLOCK, THOSE ARE THE AREAS OF THE BRAIN THAT ARE RESPONSIBLE FOR HALLUCINATIONS.

"Hallucinations..." Sherlock breathes. "So you're saying I haven't been unable to hear or see anything but you just because of some strange twist in my circuitry..."

John nods. YOU'VE BEEN ACTUALLY SEEING ME AND HALLUCINATING THAT YOU CAN'T SEE ANYTHING ELSE. OR HEAR ANYTHING.

Sherlock has to stop himself from yelling. "The HOUND drug!"

IT MUST BE. John agrees. WE MUST HAVE MISSED IT SOMEHOW.

Sherlock grabs John's hand and starts dragging him to where he hopes the doors are. "We have to go back, we have to work on this right away."

John doesn't move. IT'S AT HOME. I DIDN'T FEEL SAFE LEAVING IT IN THE HOSPITAL, IT'S LOCKED UP AT HOME AND I WAS GOING TO SEND IT BACK TO MYCROFT.

Impulsively, Sherlock grabs him and kisses him, not caring who sees, and nearly lifting the doctor off his feet. "Brilliant!" he says gruffly, and John straightens his clothing sheepishly, but looks pleased.

WE'LL START WORK RIGHT AWAY. NOW WE KNOW WHAT TO LOOK FOR.

Sherlock opens his mouth to reply but is stopped by a cold spray right by his face. It hits John too and John sneezes.

BLOODY WOMAN JUST PUT ON HER PERFUME IN THE TUBE, TOOK OUT HALF A DOZEN PEOPLE. John tells him. SOME PEOPLE JUST HAVE NO–

"Shut up," Sherlock whispers, harshly. He's trying to think. This means something, he's sure it does, he just has to put it together and for that he needs no distractions. Out of habit he squeezes his eyes shut and puts his hands to his temples.

 _Perfume, it is, the sickeningly sweet smell is all around, it's not cheap, it's good stuff, French, but over-applied and it's blown out his sense of smell completely, there's something about the aerosol, something about dampness, now he remembers, he remembers three days ago, being sneezed on in the street and nearly killing someone because he'd thought he'd been attacked, it was disgusting, another kind of aerosol, and then before that four days, he'd been in the tube again, a student had sneezed on him that time too, right in the face, he'd listed it for John as one of the things that was different but neither had taken it seriously, yet 12 hours after each he'd started to lose things, or hallucinate that he was, oh it fits together now in his head coming together with a satisfying click..._

"John," he says very quietly, "I think that–"

John jumps at his voice. WHAT? DON'T SCARE ME LIKE THAT!

"I think that..." he pauses. John doesn't look right. He's flickering and has taken on a defensive posture, his eyes darting around as if expecting danger. "John, how do you feel?"

TO BE HONEST LIKE I JUST DRANK A POT OF COFFEE. I'LL BE GLAD WHEN WE'RE OFF THE TUBE, I DON'T TRUST ANY OF THESE PEOPLE. AND THERE ARE SOUNDS. LIKE WINGS.

It's just like it was before, back in Baskerville. Whatever it's done to Sherlock is different this time, but John's reacting exactly the same. And Sherlock suspects it's not going to improve. No odd movements that would indicate any effects on those around them. It's not the drug itself that's been sprayed.

He grabs John's arm, not daring to say as much aloud, not with the perfume-sprayer still on board. He taps the letters out hurriedly.

JOHN. LISTEN TO ME. DON'T SAY A WORD. IT IS THE HOUND DRUG AND IT'S AFFECTING YOU. THERE'S A CATALYST, BUT THIS TIME THEY GOT YOU TOO AND NOT JUST ME. YOU'RE GOING TO START HALLUCINATING AND FEELING AFRAID, JUST LIKE BEFORE. REMEMBER IT'S NOT REAL. YOU HAVE TO CATCH THAT WOMAN AND GET HER PERFUME BEFORE THE DRUG REACHES PEAK STRENGTH OR I DON'T KNOW WHAT WILL HAPPEN. WE HAVE TO GET IT HOME SO WE CAN FIND OUT HOW IT ACTIVATES THE HOUND DRUG AND STOP IT. DO YOU UNDERSTAND?

John takes all that in, wide eyed, and Sherlock starts to worry he's too far gone. But then he nods sharply and, without warning, dives away, out of Sherlock's range of him, and Sherlock's world plunges back in the complete darkness and the swaying of the tube car. His lifeline is gone and he's alone on the speeding train.


	7. Chapter 7

No sooner has John left him than the train begins to slow for the next stop. Suddenly, Sherlock can picture it all with frightening clarity.

 _John's gone after their assailant but the car is packed and even if John is starting to lose his grip, he still probably knows better than to tackle an unarmed female in a closed environment and try and take her perfume, dozens of people would stop him and his story would sound crazed, but she knows she's been spotted, she'll get off and try to lose him, John will follow, has to follow, if he has any hope of getting her where he can get the substance off of her and get away with it, if Sherlock doesn't move now he'll be left behind..._

He suppresses the urge to shout John's name. He can't risk distracting him or tipping off the woman even more. When they stop he listens for the doors and tries to move towards them in the press of the crowd but he's not fast enough, not without making a fuss. They close when he is still several metres away.

Sherlock's now alone on the tube and not at all sure where he is.

 _He should have been paying attention, he was paying attention, just not to the stops, he was observing the people, he should have been doing both, why was it so hard to do both, how many stops had it been, it was five stops to Baker Street from Bart's, it had been more than one surely, but had this last been number three or four, it wouldn't have been five, John would have said, wouldn't he, but he was distracted too, Sherlock'll never get home if he gets off at the wrong place..._

It's infuriating that something so simple has become such a massive problem for him. Just when he was starting to feel like he had some control, John steps away and he's instantly helpless again. He could use the voice command on his phone to call Gordon or Mrs. Hudson and shout into it for help hoping it had connected and they can figure out where he is, but it wouldn't be exactly be inconspicuous and would definitely be utterly humiliating if not downright dangerous to expose himself that way.

He doesn't have time to deliberate any longer. He has to make a decision. Three stops, he decides. They must have gone three stops, then the fourth was where John and the attacker got out. Baker Street must be the next stop.

Sherlock has to trust that his unconscious mind has put this together for him correctly, that it's not just a shot in the dark. He maneuvers himself closer to the doors so he won't miss his chance again and braces himself for the stop. When he feels the jolt, he steps forward with the crowd, letting them carry him along.

 _Mind the gap, mind himself, mustn't appear to fumble or flail, head down, shuffle along like one of the herd, he can blend in when he needs to, be surprisingly unnoticeable for a man of his height, if he stays with largest group he should be all right, he's taken this route a thousand times before, sometimes without thinking about it at all, he'll be working on a case and find himself at his own door with no memory of the way home, this should be easy..._

There are three exits to the station, Sherlock remembers, and he wants the main one, the one that comes out on Marylebone Road. It's straight up the stairs and out, isn't it? Or is is a left? Why can't he remember? This certainly smells like the right station, that's hopeful. Sherlock decides to stick with the greatest mass of people, the correct exit for him would be the most popular. He keeps in the densest portion of the crowd, going up and notices that his hands are shaking and that his heart is pounding.

It's just the stress of the situation, he tells himself. But he knows it's not. It's the drug working on him, working whatever terrible havoc it's got for him this time. He's got to get home before it sets in. Last time he'd had twelve hours, but maybe he's been dosed so heavily, so many times, that no longer applies.

 _It's just a hallucination, all of it, the fear, the blindness, the deafness, if he can just focus he can overcome it, there are sights and sounds and people all around him, his eyes see it, his ears hear it, his brain just doesn't know, concentrate, pull back the the darkness, glimpse the world again..._

It works, just the tiniest bit. If he pours every last ounce of his focus into his eyes he can make himself see something. Flashes. The edge of a coat, a beam of light, a railing, a pillar, a neon sign. A mosaic of random impressions for just a few fleeting seconds, it's such a relief but it takes everything he's got and it hurts inside his mind and-

Boom. He trips on the rim of a step and would have hit the concrete were it not so crowded, instead careening into several people and taking out several more with pinwheeling arms trying to keep himself on balance. He can imagine the outraged exclamations around him and murmurs appropriate regrets as he steadies himself, once again in total darkness and out of the flow of traffic. He stops and tries get his bearings, trying to pick up the vibrations again to determine the direction of the majority. Suddenly a hand grabs his elbow forcefully and turns him about a quarter turn and gives him a little shove.

Before he can collect any data, the individual is gone and Sherlock is smacking into a set of doors. Relieved, without too much time to wonder about his benefactor, he pushes through and emerges in the less-than-fresh air of a London weekday morning. He walks just far enough out to avoid being slammed into by others coming through the doors and stops, lifting his head and inhaling deeply.

 _Smell of the busy road, the warmth of the underground from grates below, the awful falafel cart on the corner, sun slanting against him weakly from the left, steady vibrations of the buses that stop here, directly in front of him, less traffic to the right, he's made it, Baker Street is only steps beside him, cross it, another right, 449 ft down the sidewalk, 136 of his strides, give or take, then he'll be home, and John will be there too, he has to believe that, and he'll find a cure for them both before whatever's going to happen next is permitted to do..._

He falls in with people again, cautiously, to navigate to the corner and cross Baker Street. But once the light changes and he feels the people around him step forward he can't take it any more. He breaks into a run, gambling that the traffic will obey the signs, heedless of obstacles and pedestrians. He makes the turn and speeds up to a dead run. Most people will be coming the opposite direction this time of day and they'll just have to get out of the way. Miraculously, he mows no one down before skidding to a stop the second he whiffs the greasy bacon and burnt coffee smell of Speedy's emanating from the buildings to his left.

Sherlock scales the steps, fumbles for his key, and is up the hall stairs like a shot, all but tumbling into the safety of the flat. "John! John!" he yells, bursting through the door and scanning with useless eyes. No flash of light. No John.

 _What if John doesn't come back, what if he's been captured, or worse, and Sherlock is left here alone, waiting, until the inevitable, until he loses something else, or maybe everything else, is that the end game, to kill him, or just to humiliate him to the point where he does it himself, well, he'd already gotten to that point and he's not going back there, so anyone who wants to finish the job will have to come find him, but he'd rather John found him first..._

He sits on the rug in the middle of the room, panting, and tries to pull himself together. His heart is beating so fast. It is just adrenaline and exertion, or something else? No telling what the next effect will be. But he has time, he tells himself. He should have time. He quietens his breathing and slows his heart as much as possible. If John isn't back in one hour, he decides, he'll call Grant and set the police looking. But he senses that would be something of a nuclear option with whoever they are dealing with, so best not until it's clear John's not going to make it on his own.

Sherlock closes his eyes and draws up the image of their flat in his mind palace, as he had last seen it the morning they'd set out after the cat burglar. He waits until he has every detail in place, every discarded book and tea mug and coat on the coat rack and then very slowly opens his eyes, willing himself to see it, willing it to be there.

 _And it's there, faintly, but it's there in its totality, and not just a protection from the way he remembers it, he's seeing it as it is now, cattle skull leaning against the wall needing to be remounted, lamp gone, clothes and dishes everywhere, more of mess even than usual, he's penetrating the fog of the nil, the anti-hallucination, just for a moment, now it's flickering, and he's got to try and hold it but..._

"Gah!" he cries aloud before he can stop it, suddenly feeling like a railroad spike has just been driven through his skull. He grabs his head, curling in on himself and squeezing his eyes shut as if that will shut out the pain. It ebbs away, not nearly fast enough, and he straightens back up, gasping for air again. Better save that for a last resort, then, lest he give himself an aneurysm.

He rubs his temples and then taps his fingers on the floor nervously, waiting, wishing he could do something, anything. The minutes drag on and he's just about to make the call when he hears the door downstairs crash open. Sherlock jumps to his feet just in time for John to blow into the room like a solar storm.

 _John's bright, too bright, crackling with live current, pupils dilated, aura arcing out of control, shading into colors so high in the spectrum even Sherlock can't make them out, energy flying everywhere, he almost wants to duck to avoid it as it lashes toward him, and it feels different, it's not just sight but feeling and sound like he's standing in the middle of a thunderstorm made entirely of lightning..._

"Sherlock," John gasps, gulping for air. He's so clearly outlined now, more clearly than in real life, that Sherlock can read his glowing lips.

"Did you get it?" Sherlock demands, watching him through narrowed eyes, trying to assess too much data with too few functional senses. John looks like he's developing a black eye, there are some cuts on his face and knuckles, but nothing seems serious and John doesn't seem to have realized he has them.

John nods not even noticing that Sherlock doesn't need Morse anymore, and tosses him a small glass vial with an old-fashioned aerosol pump. His eyes are darting back and forth, not scanning like Sherlock's do, but orbiting madly, as if seeing too many things at once. Likewise his whole body is tense, twitching, jumping wildly on a small scale. He's trying to keep himself in check, but it's not going well, Sherlock decides.

"The Hound drug?"

"Upstairs. Lab freezer with padlock."

Sherlock nods curtly. He takes a step towards John, almost flinching at the charge and heat that surround them both, and wonders if this part of what the drug is doing to him now. He puts his hands on John's shoulders and they tingle.

"John, it's not real, remember? It's like before. It's the drug. You're hallucinating."

John breathes in very quickly through his nose several times. "The sounds..." he manages. Sherlock can't see any colors other than John's angry aura, but he'll bet his friend is white as a sheet and his skin is obviously clammy.

"What sounds?"

"War. The battle. It's outside. Sherlock, they're coming..."

 _The war, of course it would be the war, in the absence of any other input or threat John always goes back there, he's never really left, it's a powerful memory, a fear he's never truly recovered from, impossible to counteract, Sherlock can only hope to distract..._

"No," Sherlock tells him firmly. "No one is coming. You have to focus. We are in Baker Street. We have been drugged. I need to you help me make an antidote. Listen to my voice, John. Am I telling you the truth?"

John nods, a little uncertainly.

"Good." Sherlock has to stop then for a moment. His own brain is starting to feel fuzzy. Maybe it's because he's been on overdrive for so long, or maybe this is the beginning of the next effect of the drug on him. Or maybe he's just being paranoid. He continues, with effort. "And am I real?"

John nods again, licking his lips and looking around before answering. "Yes. Yes, you're real."

"And so are you. You're John Watson."

"And you're Sherlock Holmes," John replies. Sherlock is so very glad John's said that because it felt like he might have been starting to forget.

 _He's Sherlock Holmes, that's the one thing he can't ever forget again, and he and John have to make a cure, those are the the only things that matter, identity and chemistry, everything else can be taken, as long as he has those two things he can get the rest back, he'll recite the periodic table on a loop if he has to, run combustion experiments in his mind's eye, repeat his name over and over, anything thing not to lose those two most precious bits of knowledge..._

"We haven't any time," Sherlock says, trying not to let urgency shade to panic. That's the last thing John needs to hear in him. "I need you to block it out. It's all a hallucination. I need you to block it out, Dr. Watson!"

"Okay," says John, making a visible effort to pull himself together. He cycles through colors like a nervous chameleon. "Just tell me what you need."

Sherlock follows John's up the otherwise dark stairway to the lab. He hasn't tried to see anything else again, and for now the wattage John is putting out is enough. John retrieves the drug from the freezer and sets it on the lab bench along with the reports from the hospital and the fake perfume vial.

"I need you to read me the report from Caroline," Sherlock orders. "Don't think about anything else, just read me the words on the page." Focusing enough to see the papers and read the words might just tear his brain apart, but he can watch John's lips without pain.

John does as he is told, though his words are fumbling and he cringes at sporadic intervals as though a bomb has just gone off. He's dripping with sweat now. Sherlock gives his mouth rapt attention, afraid he'll misread something but knowing John is in no condition to code and read at the same time right now.

"Wait, wait," Sherlock cries. "What was that? Go back! Maya something?"

John slows. "...interference or obstruction of the the myelin sheathing on the primary temporal lobe neurons and adjacent..."

"Myelin! What's that? I know that word."

 _Why can't he remember, it has to do with the brain, obviously, he's no neuroscientist but he's studied more than his share of brains, but right now he can't remember a thing about any of them, why had he even bothered, they were just squishy grey matter, the people in them long gone, it had seemed so important at the time..._

There are gaps in his knowledge, Sherlock realises. And they're getting bigger. But before he has a chance to let that thought sink in and truly unnerve him, John leaps out of his stool, landing in a half crouch facing the door and brandishing the stool as a defensive weapon.

"John," Sherlock says in what he hopes is a calming tone, for both their sakes. "What are you doing?"

"They're in the house, Sherlock," John says. "My God, I don't have my gun. Okay, you go out the window, I'll hold them off!"

"John, there's no one. Try to remember."

 _Sherlock tries to remember too, there is no one, of course, it's all in John's head, but there's something wrong with Sherlock's head too, what if he's the one who's imagining it, functionally deaf and blind, unable to detect the advancing army, the warzone outside, wouldn't John know better than him if they were under attack..._

No, that's wrong. There's no war. John is being influenced by the drug. Sherlock concentrates with difficulty. "You were explaining to me about myelin."

John shakes his head, wide eyed. "No, they're almost here. Please. Please Sherlock, run!"

 _He almost does it, it would be easy to slip into that world, easier than formulating a counter measure to a drug he doesn't understand with a mind that's betraying him by the moment, running is simple, fight or flight, but no, wait, that's not what they need here, the harder way is the true one, it always is..._

"Soldier!" Sherlock bellows. "Sit down at once!"

John freezes for a long moment and then to Sherlock's great relief replaces the stool and sits back down, though he's still casting worried glances at the door.

"Ignore everything outside. Ignore everything but what I tell you to do and we will survive this," Sherlock says with more surety than he feels. "Now, what is a myelin sheath?"

John calms visibly as he accesses his medical memory. If Sherlock can just keep him working John might be able to avoid another break entirely.

 _But will he be able to avoid one himself..._

"Myelin is like an insulator for your brain," John tells him, tugging at his hair and ears repetitively and cracking his neck like a tic. "It forms around your neurons, it protects them and keeps everything from going haywire. Without it..."

"Very bad things," Sherlock finishes and John nods, digging his nails into his palm. "If something were to interfere with the myelin, would that be enough to cause the problems we've been seeing?"

"Yes. No. Maybe? I can't be sure..." John's fear is palpable and it's starting to get to Sherlock. He can't fight fear and loss of brainpower at the same time.

 _The knowledge is in there, nothing can take it away, it can only be blocked not erased, not really, even if he tells himself otherwise, he has to trust his mind, he's spent 36 years putting the data in, it knows the answer even if he doesn't..._

"The mercury," Sherlock says slowly, the word feeling alien and thick on his tongue. "It's in the adjuvant but not the Hound drug. It reacts with the... the... things.. organophosphates... in the drug and precipitates out to create a... coating. What's it called? Conductive film, a build-up on the myelin sheaths that impairs or disables their ability to function. It makes the effect of the drug unpredictable... and lasting. Everything goes..."

"Haywire," John finishes, his eyes glassy and terror-filled.

Sherlock's not even sure he's understood what he's just told John, but he knows it's right, somehow. He nods.

"So, that means for me, now..."

Sherlock hesitates, partly out of reluctance to tell him and partly from the sheer inability to locate the words. Finally they tumble out without consulting his consciousness. "If we don't find a way to dissolve the coating you will remain in your... paranoid hallucinatory state until your body is unable to sustain it and you will..."

"Die of fear."

"Essentially."

 _But John mustn't die, Sherlock won't let that happen, he's got to get them through this, he's got to work harder and harder until the answer comes, he's not sure what would be worse, to live without his knowledge or without John or perhaps without even knowledge of John..._

"And you?"

His head is pounding now, the headache having crept up on him as his memory crept away. "I don't know. It's working slower on me but thinking is becoming difficult and I am feeling... some sense of irrational fear as well."

"I'm not sure it's irrational," John says, his face grim. "Okay. Let's work, before it gets worse. I'll be your hands, you be my mind."

Sherlock pushes through the fog to the lab in his mind palace and finds it mostly clear and workable. He moves quickly inside of it, breaking down every chemical from both compounds, reassembling them, reacting them with other chemicals until something starts to happen.

 _He's in the lab, the lab in his mind, the lab in his home, he's with John Watson, and he's Sherlock Holmes, has there ever been anything other than this, has he ever existed outside this place, outside of numbers and formulae and acids and ions, he can't remember, he has to find a cure to something, he has to nullify the drugs, but he can't remember why that is, what came before this or what might happen after..._

"Alcohol" he tells John, with difficulty, not at all sure the word is the right one. "Start with alcohol."

John follows his instructions to the letter, despite the fact that his whole body is shaking. His hands are shaking too, but not so badly he can't use them. They always were the steadiest part of him in a crisis. John works and Sherlock talks, knowing his voice might be the only thing keeping John from disintegrating entirely.

 _Keeping Sherlock from disintegrating entirely, his voice might as well be coming from another place entirely, a distant entity telling them both what to do, like an echo of himself when he was whole, coming from deep inside, from a place the drugs can't touch..._

"Add the ionized bromine in equal parts with the solvent," Sherlock tells John watching him and realising he wouldn't even know if John was doing it wrong. "Now, heat it to 435 degrees Celsius for fifteen seconds and then supercool it immediately with liquid nitrogen. If I'm right... we're right, this should simultaneously neutralize the remaining drug in our systems and dissolve the coating that's interfering with the neuron function."

 _Did that even mean anything, was he making all of this up, just how impaired is his mind right now, for all he knows they might have just synthesized the most potent of poisons or a psychoactive drug or a new recipe for candyfloss, how can he trust either of them in this state, but there's no one else to trust and it's too late to do anything but go forward so he feigns the confidence, the knowledge that has always come so easily to him..._

"And then we'll have free-floating mercury in our systems. Great," John says, and his sarcasm is oddly comforting. Even paranoid and crazy, he's got a sharp tongue.

 _Mercury, is that a bad one?_

"The mercury ions will be coated by... stuff... as they are removed and pass harmlessly from our bodies," Sherlock finds himself saying. Then he adds, "I hope."

The cooling tank beeps before John can give him a horrified look.

"It's done." Sherlock says, not at all sure that it is. But it had better be because even the memory of the knowledge is fading, he wouldn't know mercury from what's-it-called if they both him in the face. "Now, to test it."

"Test it? You mean on us?"

"I don't see an alternative."

 _That doesn't mean there isn't one, just that he can't see it, but he can't articulate that to John right now, can't expect John to do the thinking, it's all John_ _can do to keep himself from having an all out nervous breakdown without Sherlock adding to his panic..._

John shakes his head as if trying to clear it and failing over and over. "You're right. I can't last at this heightened state much longer. My heart...adrenaline is a poison you know." His breathing is labored, and Sherlock is glad he lacks the resources to consider what might be going on inside of John right now. "If they don't shoot me first, my own body will take me out. Either way, we've only got a few minutes. But you, genius, you didn't think about delivery method did you?"

Sherlock blinks at him. "What?"

John takes out a syringe that is frankly alarming in size. "Well, it needs to be delivered directly to the brain to have enough potency to work. There's not a lot of options." He draws half of their potion into the syringe and stands.

"John, don't be rash. Think this through," Sherlock says, backing away slowly.

"One shot. Directly to the brain. No second chances. Before they come and kill us. Or worse." John tells him. "It's the only way to be sure. Better than being captured. Trust me."

John looks like a wild thing, a drug addict that's just overdosed, a mental patient, still jumping at imaginary noises, starting at shadows that aren't there, expecting the invasion that isn't coming. He's approaching Sherlock like a mad scientist, unstable and desperate but determined.

 _And Sherlock can't think, there's got to be another way, but he can't think of it, he's not a doctor and his processor is grinding to a halt, and it's John, hallucinating, terrified, crazed, but still_ _John, if there's anything left in the world for him to hang on to, it's John Watson, even half way to insanity he's worth ten men, and he's all Sherlock can see..._

Sherlock find himself also shaking and sweating nervously, and he's not sure he can blame it all on the drug. "If you miss..." he says.

"You die."

Sherlock nods, his hands still up to ward off the needle.

"I won't miss," and there's a glint in John's eye and a brief stabilizing of his right hand that says no, he won't miss. "And I won't let them get you."

 _And Sherlock knows he won't, John will sacrifice himself to imaginary armies, to the hordes of all his nightmares to keep Sherlock safe, over and over again if necessary, and at the end it's the only thing Sherlock knows any more and somehow it's worth all of his lost knowledge, ten times the value_ _of it, and everything inside of him is very, very calm..._

Sherlock puts his arms down. This is how it ends, one way or another, his life in John Watson's blazing, shining, electric hands. He doesn't know much right now, but he knows he could hardly want it to be any other way.

"What about you?" Sherlock asks.

"I'm the surgeon, remember? You first." And with one jerky, impossibly fast movement John leaps wide-eyed towards him and grabs the back of his neck with one hand, driving the long, fearsome needle upwards, deep into Sherlock's foramen magnum with the other. Sherlock's world shatters with pain and then, blessedly, melts into darkness.


	8. Chapter 8

Sherlock wakes slowly, to a splitting headache and a mouth that feels like the entire contents of the Sahara have been emptied into it. The first thing he notices is that there are sounds.

 _Blood rushing through his own veins, muted traffic outside, even the quiet of the room has a sound that's quite distinct from utter silence, and there's breathing too, human breathing beside him, loud as a waterfall in his ear..._

Sherlock remembers. His eyes fly open and the brightness of even the very dim upstairs room is dazzling, almost painful. He can see again, in normal colors, everything around him. The ugly plaster ceiling is nothing short of an artistic revelation. It worked.

He's sprawled on his back on the wood floor of the bedroom-cum-lab, and he turns his head painfully to see John beside him, a few feet away. John is face down, unconscious but breathing deeply, pulsing with a soft anaemic glow around his prone form. There is a three inch needle sticking out of the back of his head and an accompanying dried trickle of blood down his neck that makes Sherlock shudder involuntarily and reach behind his head to feel the deep bruise in the same spot.

Sherlock sits up slowly, a little at a time, drunk on the vastness of sensory input flooding his brain. He leans over to check John's vitals, just to be sure. He's fine.

 _John had saved them, saved them both, of course he had, it's what John's for, Sherlock should never had doubted, never will again, can't believe they came through such a horrific ordeal mostly unscathed, physically if not psychologically, Sherlock wonders what the damage will be there, but it doesn't matter because they have each other and that will get them through as it always does..._

He leans over and carefully removes the needle from John's neck, staunching the fresh flow of blood with his shirt cuff. John flinches just the barest bit in his sleep but doesn't wake. He looks like he will sleep for a long time now.

Now that the immediate danger is over, Sherlock's thoughts instantly turn to the cause of all this. He hadn't had time or means to think about it before, when just surviving took all of his mind and energy, but now it's all he can think of. He closes his eyes, creating a blank slate on which to project the data and sense memories of the past week. There has to be something there, something he can use.

 _Sneezes, perfume, sensations in the crowd, on the Tube, people walking by, jarring him, touching him, very specifically not touching him, the sense of being watched, being analysed, being alone in the hospital but not alone, an unseen presence, just out of reach, out of smell, out of taste, floating in the back of his mind, so small as to be unnoticed, unnoticeable, except in concentrated memory, except for one time, one small moment that had sealed his fate..._

Sherlock's eyes fly open and he inhales in one startled breath, "The man in the train station!"

His eyes scan, trying to remember everything. There wasn't much to go on, it was only for an instant that the stranger had hands on his coat, pointing him in the right direction, saving him. But the instant was enough. There was a scent, a distinct odor, almost a taste, under the cologne and detergent and aftershave, a scent that is forever seared into his nostrils.

Sherlock sets his jaw grimly and clambers to his feet. Gently, he hoists John in his arms and carries him, a little unsteadily, down the stairs, depositing him on the sofa.

He feels surprisingly reluctant to leave John, something in him stubbornly protective of him even though the danger has passed. At least for now. Without meaning to, Sherlock brushes John's hair off his forehead and plants a lingering kiss there even though John will never know. Then he dons his coat like a suit of armour and leaves the flat, forcing himself not to look back at the sleeping form on the sofa.

 _John will be safe for now, for a given value of safe, it's not John that's wanted, it was only to get his attention, it makes it almost worse, the endangering of John, to get to him, it keeps happening, it will always happen, and John bears it but Sherlock's not sure if he can much longer..._

Reversing the route that mere hours ago had left him feeling as lost as a man in a jungle is now so simple as to require almost no thought at all. He rides the Tube the requisite five stops, hops off, enters Bart's, and hits the elevator button for the roof without even having to consider a single step of it. It's a luxury, he knows now.

Once at the top he settles himself on a electrical box and lights a cigarette. He doesn't have long to wait.

"Took you long enough," drawls a familiar treble.

Sherlock doesn't look at the man. Instead, he contemplates the city sky line in the slanted afternoon light. "2.7 minutes after I regained my faculties. Disappointed?"

"In so many things." Moriarty slithers over and takes a seat beside him. Too close, but Sherlock refuses to give him the satisfaction of moving away. He hand rolls a cigarette with studied leisure and Sherlock holds out his own for Moriarty to light it off. The master criminal takes a deep drag and lets out an almost obscene sigh of pleasure. "You don't seems surprised to see me."

 _He's not, as soon as he put it together it was clear it could only ever have been Moriarty, it was practically a love letter, deconstructing him like that, watching him struggle, allowing him to be saved at the last minute instead of doing him in, so carefully orchestrated to bring him here..._

"Mycroft keeps me informed. I'm impressed you managed to orchestrate something so elaborate so quickly after regaining your freedom."

"Ah, Mycroft Holmes. Now he is absolutely no fun at all, no wonder you can't stand each other. Still, he gave me quite a lot of useful information during my interrogation. Almost worth the terrible housing conditions and light torture."

Sherlock can't stand to be so close to him any more. He jumps to his feet and spins to face Moriarty. "All right, so tell me why? What was the plan?"

Moriarty laughs and finishes his cigarette, throwing it to the ground and not bothering to stomp it out. "Plan? My dear Sherlock, I just wanted to see what would happen. The events at Dartmoor were relayed to me in vivid detail. I wanted to see for myself. I had hoped to reproduce the effects of the drug, make them permanent, or at least as permanent as I wanted them to be, see what you would do then. Alas, I couldn't procure a sample of my own in that time and my chemists are...well, they're no you."

"You could only hope to activate what was left in my system through the adjuvant," Sherlock mutters, half to himself.

 _It's brilliant and awful and wonderful, something Sherlock would do, only not on someone else, even without John he's got some scruples, but dear god wouldn't it be nice not to have sometimes, to be able to do anything in the world just to see what would happen, maybe then things wouldn't be quite so boring..._

Moriarty nods knowingly, as if he can see what's going on behind Sherlock's eyes. "It didn't work as I'd expected, but may I say the results were far more entertaining. Loss of senses. Loss of self. I had hoped under a strong psychosis you might kill John Watson. I never dared to hope you might try to kill yourself. Of course I would never have let that happen. You're not to die until I say so. John, on the other hand... the sooner the better, really."

Quickly than a flash Sherlock is on him, has Moriarty's lapels fisted in large hands and his feet nearly off the ground. "Why?" he growls, shaking the smaller man.

Morarity is unfazed. He practically laughs in Sherlock's face. "Because you think you belong to him, but you don't. You belong to me."

Sherlock releases him, pushing him away in revulsion. Moriarty stumbles, laughing for real this time. "You're delusional," Sherlock spits, turning away.

 _Is he delusional, Sherlock's not so sure, obviously he belongs to John, but Moriarty is in his head too, chained and locked up tight, but why the need for so many locks if what he's saying doesn't have a a bit of truth to it, what reason to be afraid if Moriarty isn't, at least a little bit, right..._

"Am I?" Moriarty echoes his thoughts uncannily. "You can't tell me you haven't felt it, ever since the first time, since dear departed Carl. He was my first gift to you, when I realised I wasn't alone in this world. We've been connected intimately, spiraling ever closer to each other in this courtship dance of ours. We're the same, two sides of a two-headed coin. We belong to each other. We're the only ones who ever could. But you, you think you belong to John Watson, to a common tart, a lap dog who barely deserves the title. I can't have that, Sherlock. It makes me look bad."

Sherlock spins back to look at him incredulously. "You actually believe all this, don't you. That we have some kind of... what? Destiny?"

 _Destiny, there's no such thing, but it would be so easy, to let go finally, to stop resisting the dark, to stop resisting who he is, being good is so hard and he's so bad at it sometimes he wonders what the point is, he'd promised John not to listen to the darkness again, but this is different, this feels like part of his soul, the part he's always told himself he can't accept, the man he must never become, but he can't pretend it's not alluring, all that power before him, all the things he could do if he simply stopped caring..._

Moriarty grins and approaches him with a predatory air, confident. "Tell me you don't feel it at all, Sherlock. We were made for each other, and this world was made for us. Think what we could do together. How exciting it could be. We could take this world and dismantle it brick by brick." He's standing very close to Sherlock now. Too close. Sherlock can feel the heat pouring off his body. "We could take this world and burn it into ashes just for something pretty to look at."

"That's not me," Sherlock says, but his voice lacks conviction. Moriarty's lithe little body is pressed up against him, and he's pure sex looking feverishly up into Sherlock's face, and just for a moment, Sherlock feels it like a thunderclap.

 _His body is responding and he doesn't want it to, but part of him does, part him feels the connection, the sameness, and it's terrifying and exciting and alluring, they could be gods together, they could do anything, rule anything, have anything, have each other, and it would be thrilling like nothing else has ever thrilled before, like nothing else could, like John never could, they could fuck and fight and kill and take until they burned the whole world out and finally burned each other out and it would be mad and glorious and spectacular and wrong and he wouldn't even have to care..._

Moriarty sees him waver, smiles wolfishly, and goes up on his toes. "We can even let Doctor Watson live, if you like. He does make such a good pet." He presses his lips to Sherlock's, running his tongue enticingly along the crease of Sherlock's mouth. But he's too late. He's made a mistake.

 _Part of him wants, he can't deny, the power, the excitement, the passionate hate, the wrongness that could be so right, Moriarty is seductive and a part of him was born seduced, but John, John is good and John is his and nothing in the wide universe that threatens that, that threatens John can ever, ever have him, and John's name in Moriarty's foul mouth turns his stomach, John makes him good, John keeps him here, and even his most base urges, his darkest desires crumble in the light of that fact, breaking the spell..._

Sherlock give a tiny, distant smile when Moriarty pulls away, visibly surprised at the lack of response. He straightens and steps back from his foe.

"Do you want to know how I knew, for certain, that it was you?" Sherlock asks mildly, as if inquiring about the weather. "The train station. Did you give yourself away on purpose?"

Moriarty cocks his head in genuine confusion. "You couldn't have known. I changed everything. You were deaf and blind."

"Oh yes, you changed everything. Clothes, manner, cadence of walk, all the scents of life, your cosmetics, everything. But I still smelled you under it. There's a smell to you James, that you can't hide. You smell of rot. You smell of decay. And no matter what you promise me, I am not going to rot with you."

For just a moment Moriarty looks nonplussed. Then he smiles as if he's just been told a joke only he understands. "What if I promise you that John Watson will suffer. Will die. Will know you for a thousand times betrayer before he dies. Will you rot with me then?"

Sherlock scoffs. "You don't have that power."

"Don't I?" Moriarty lets it hang there.

 _He does, or at least he might, Moriarty has more power than Sherlock cares imagine, and Sherlock has just turned down the chance to share in it, to increase it, and he's never felt more certain of anything, but still, he doubts, this is why good can't triumph, good has the right but evil has the power and there's no one more evil than James Moriarty, Sherlock knows better than anyone because it's inside of him too..._

"You can make what choices you like. You can choose your own warped version of good over my vision of greatness. You can stay in your safe flat with your single minded little soldier. You can make each other all the promises you like. But I promise you, John Watson will not have you. I'll make you break his heart. Or I'll break him. Your choice, Sherlock. Isn't it nice to have choices? Make yours carefully, you won't have a chance to take it back."

Without even the smallest of tells beforehand, Sherlock launches himself at Moriarty only to pull up short at the flash of a laser sight in the corner of his vision. Sherlock freezes.

"Uh uh," Moriarty scolds. "Not yet. But it won't be long. Go home, Sherlock. Hold your Doctor. Make your choices. And don't say I never gave you anything."

Sherlock barely has time to blink before Moriarty is gone. He straightens and walks to the edge of the roof, as sunset just begins. He smokes three more cigarettes in silence and then goes home.

John is still asleep when he gets there. Thankfully. He could never explain where's he's been. John must never know.

 _He can stop it, he has to, Moriarty isn't playing this time, he means what he said, but Sherlock has an advantage, he has that evil in him, he knows how Moriarty thinks, what he wants, but there's no goodness in Moriarty, no Sherlock in his mind, Sherlock never believed in his goodness before John and still doesn't some days, but it's the only hope to save them both, to keep what he has, so he has to believe it now..._

Suddenly exhausted, he carefully crawls up on the sofa alongside John, slipping an arm underneath him, encircling his rib cage and holding him tightly. It's not long before John stirs, then starts awake.

"Wha- where-? Oh. Sherlock." He flickers from high intensity sparking to low, mellow warmth when he identifies Sherlock beside him. His voice is pure relief. "It worked. Thank God. How did we get down here? Are you okay? Why are you holding me so tight? It hurts. Jesus, everything hurts."

Sherlock releases some of the pressure he didn't realise he was applying and feigns grogginess. "Sorry. Don't know. Don't remember," he lies. "I can see and hear again though. Everything appears normal."

John lets out a long breath and digs his fingers into Sherlock's hair, reaching across to rub Sherlock's upper arm as well. Sherlock arches into the caresses like a cat starved for attention. "It's over then. I thought... never scare me like that again, all right?"

"Never," Sherlock agrees somberly. Another lie.

 _Whatever happens in future, even in the best case, it's likely to scare them both more than anything ever has, even this, but pretending is the only way they can live..._

John gives a wry smile and together they sit up, settling on the sofa with sides pressed into each other. John feels strangely happy, content, glowing warm light at Sherlock. the light of a candle when the power has gone out. Despite the pall over him, some of it infects Sherlock, and he smiles and lets his hand drift to John's thigh.

"So, who do you think did this to us? You're not going to let it go, I hope!"

 _Damn, he hadn't thought of that, of course John would want to know and he can hardly tell him it's Moriarty, John might do something foolish, and it's usually lovely when he's foolish, but it's not lovely if he gets himself killed..._

Sherlock pauses. "Of course not. We'll track him down. My guess is someone from Baskerville, one of the scientists we pissed off."

" _You_ pissed off. Not Doctor Stapleton, surely?"

"No," Sherlock says a little too quickly, but John doesn't seem to notice. "But plenty of people there would have had a grudge against us, and the means. Perhaps a descendant of the original H.O.U.N.D. crew. I'm sure it will become clear once we've recovered."

That seems to be enough to get John to let it go and after long moments of companionable silent Sherlock speaks. "You know, you mentioned that the antidote needed to get directly to the brain to work..."

"Yeah. Couldn't just swallow it or inject it normally. Blood-brain barrier and all that. Sorry about the massive needle to the brain. I realise it was a bit alarming. Still, only option."

Sherlock nods thoughtfully. "Don't get me wrong, I'm very grateful for your... ingenuity. And your impressive aim, especially given that you were very nearly in a complete psychotic state. The fact that you managed not to kill or paralyse either one of us is very impressive. But...considering all that and the original delivery method of the toxin, instead of risking both our lives, healths, and sanities in a dubious display of medical machismo while under the influence of hallucinatory drugs... could you not have just sprayed up our noses?"

John gapes at him. "I... I mean, we needed to be sure that... it could have... the dilution..."

Sherlock raises an eyebrow.

John sputters for a moment and then sighs. "You royal pillock, you're right. Insufferable git."

They look at each other and burst out laughing. Peals of hysterical uncontrollable laughter until tears run down John's warm, crinkly face and his aura looks like the northern lights over Iceland during an electrical storm.

"Still, I think I did rather well considering I was pretty well sure the Taliban were about to break down our door and also there might have been vampire birds after us," John points out, wiping his eyes. "I'd like to see you do better!"

 _He could never do better, not in a million years, there's nothing better in the world than John Watson in the darkest night of the soul risking both their lives to save him..._

Sherlock has no words to express what he's thinking at the moment, so he settles for bumping John's head gently with his own. "Don't ever go out," he says.

John gives him a funny look. "I won't if you won't," he says. He leans over and takes Sherlock's mouth in his own, as tender as anything Sherlock's ever felt. It goes all all golden in Sherlock's head and he lets himself forget, just for a moment everything that's happened today or might happen in the future, and surrenders to the bright galaxy that lives inside John Watson's skin.


End file.
